One of the symptoms of conduct disorder is a lower level of fear. Research performed on the impact of toddlers exposed to fear and distress shows that negative emotionality (fear) predicts toddlers' empathy-related response to distress. The findings support that if a caregiver is able to respond to infant cues, the toddler has a better ability to respond to fear and distress. If a child does not learn how to handle fear or distress the child will be more likely to lash out at other children. If the caregiver is able to provide therapeutic intervention teaching children at risk better empathy skills, the child will have a lower incident level of conduct disorder.

There are no specific criteria for "externalizing behavior" or "externalizing disorders." Thus, there is no clear classification of what constitutes an externalizing disorder in the DSM-5. Attention-deficit/hyperactivity disorder (ADHD), oppositional defiant disorder (ODD), conduct disorder (CD), antisocial personality disorder(ASPD), pyromania, kleptomania, intermittent explosive disorder (IED), and substance-related disorders are frequently referred to as externalizing disorders. Disruptive mood dysregulation disorder has also been posited as an externalizing disorder, but little research has examined and validated it to date given its recent addition to the DSM-5, and thus, it is not included further herein.

Externalizing disorders often involve emotion dysregulation problems and impulsivity that are manifested as antisocial behavior and aggression in opposition to authority, societal norms, and often violate the rights of others. Some examples of externalizing disorder symptoms include, often losing one's temper, excessive verbal aggression, physical aggression to people and animals, destruction of property, theft, and deliberate fire setting. As with all DSM-5 mental disorders, an individual must have functional impairment in at least one domain (e.g., academic, occupational, social relationships, or family functioning) in order to meet diagnostic criteria for an externalizing disorder. Moreover, an individual's symptoms should be atypical for their cultural and environmental context and physical medical conditions should be ruled out before an externalizing disorder diagnosis is considered. Diagnoses must be made by qualified mental health professionals. DSM-5 classifications of externalizing disorders are listed herein, however, can also be used to classify externalizing disorders. More specific criteria and examples of symptoms for various externalizing disorders can be found in the DSM-5.

Currently, two possible developmental courses are thought to lead to conduct disorder. The first is known as the "childhood-onset type" and occurs when conduct disorder symptoms are present before the age of 10 years. This course is often linked to a more persistent life course and more pervasive behaviors. Specifically, children in this group have greater levels of ADHD symptoms, neuropsychological deficits, more academic problems, increased family dysfunction, and higher likelihood of aggression and violence.

There is debate among professionals regarding the validity and appropriateness of diagnosing young children with conduct disorder. The characteristics of the diagnosis are commonly seen in young children who are referred to mental health professionals. A premature diagnosis made in young children, and thus labeling an individual, may be inappropriate. It is also argued that some children may not in fact have conduct disorder, but are engaging in developmentally appropriate disruptive behavior.

The second developmental course is known as the "adolescent-onset type" and occurs when conduct disorder symptoms are present after the age of 10 years. Individuals with adolescent-onset conduct disorder exhibit less impairment than those with the childhood-onset type and are not characterized by similar psychopathology. At times, these individuals will remit in their deviant patterns before adulthood. Research has shown that there is a greater number of children with adolescent-onset conduct disorder than those with childhood-onset, suggesting that adolescent-onset conduct disorder is an exaggeration of developmental behaviors that are typically seen in adolescence, such as rebellion against authority figures and rejection of conventional values. However, this argument is not established and empirical research suggests that these subgroups are not as valid as once thought.

In addition to these two courses that are recognized by the DSM-IV-TR, there appears to be a relationship among oppositional defiant disorder, conduct disorder and antisocial personality disorder. Specifically, research has demonstrated continuity in the disorders such that conduct disorder is often diagnosed in children who have been previously diagnosed with oppositional defiant disorder, and most adults with antisocial personality disorder were previously diagnosed with conduct disorder. For example, some research has shown that 90% of children diagnosed with conduct disorder had a previous diagnosis of oppositional defiant disorder. Moreover, both disorders share relevant risk factors and disruptive behaviors, suggesting that oppositional defiant disorder is a developmental precursor and milder variant of conduct disorder. However, this is not to say that this trajectory occurs in all individuals. In fact, only about 25% of children with oppositional defiant disorder will receive a later diagnosis of conduct disorder. Correspondingly, there is an established link between conduct disorder and the diagnosis of antisocial personality disorder as an adult. In fact, the current diagnostic criteria for antisocial personality disorder require a conduct disorder diagnosis before the age of 15. However, again, only 25-40% of youths with conduct disorder will develop antisocial personality disorder. Nonetheless, many of the individuals who do not meet full criteria for antisocial personality disorder still exhibit a pattern of social and personal impairments or antisocial behaviors. These developmental trajectories suggest the existence of antisocial pathways in certain individuals, which have important implications for both research and treatment.

Though the American Psychiatric Association's criteria for attention deficit hyperactivity disorder (ADHD), and the World Health Organization's criteria for hyperkinetic disorder each list a very similar set of 18 symptoms, the differing rules governing diagnosis mean that hyperkinetic disorder features greater impairment and more impulse-control difficulties than typical ADHD, and it most resembles a severe case of ADHD combined type.

Unlike ADHD, a diagnosis of hyperkinetic disorder requires that the clinician directly observes the symptoms (rather than relying only on parent and teacher reports); that onset must be by age 6 not 7; and that at least six inattention, three hyperactivity and one impulsivity symptom be present in two or more settings. While ADHD may exist comorbid with (in the presence of) mania or a depressive or anxiety disorder, the presence of one of these rules out a diagnosis of hyperkinetic disorder. Most cases of hyperkinetic disorder appear to meet the broader criteria of ADHD.

Hyperkinetic disorder may exist comorbid with conduct disorder, in which case the diagnosis is hyperkinetic conduct disorder.

The fourth revision of the "Diagnostic and Statistical Manual" (DSM-IV-TR) (now replaced by DSM-5) stated that the child must exhibit four out of the eight signs and symptoms to meet the diagnostic threshold for oppositional defiant disorder. Furthermore, they must be perpetuated for longer than six months and must be considered beyond normal child behavior to fit the diagnosis. Signs and symptoms were: actively refuses to comply with majority's requests or consensus-supported rules; performs actions deliberately to annoy others; is angry and resentful of others; argues often; blames others for their own mistakes; frequently loses temper; is spiteful or seeks revenge; and is touchy or easily annoyed.

These patterns of behavior result in impairment at school and/or other social venues.

Oppositional defiant disorder (ODD) is defined by the DSM-5 as "a pattern of angry/irritable mood, argumentative/defiant behavior, or vindictiveness". Unlike children with conduct disorder (CD), children with oppositional defiant disorder are not aggressive towards people or animals, do not destroy property, and do not show a pattern of theft or deceit. A diagnosis of ODD is also no longer applicable if the individual is diagnosed with reactive attachment disorder (RAD).

Inattention, hyperactivity (restlessness in adults), disruptive behavior, and impulsivity are common in ADHD. Academic difficulties are frequent as are problems with relationships. The symptoms can be difficult to define as it is hard to draw a line at where normal levels of inattention, hyperactivity, and impulsivity end and significant levels requiring interventions begin.

According to the DSM-5, symptoms must be present for six months or more to a degree that is much greater than others of the same age and they must cause significant problems functioning in at least two settings (e.g., social, school/work, or home). The full criteria must have been met prior to age 12 in order to receive a diagnosis of ADHD.

ADHD is divided into three subtypes: predominantly inattentive (ADHD-PI or ADHD-I), predominantly hyperactive-impulsive (ADHD-PH or ADHD-HI), and combined type (ADHD-C).

A child with ADHD inattentive type has most or all of following symptoms, excluding situations where these symptoms are better explained by another psychiatric or medical condition:

- Be easily distracted, miss details, forget things, and frequently switch from one activity to another

- Have difficulty maintaining focus on one task

- Become bored with a task after only a few minutes, unless doing something enjoyable

- Have difficulty focusing attention on organizing and completing a task or learning something new

- Have trouble completing or turning in homework assignments, often losing things (e.g., pencils, toys, assignments) needed to complete tasks or activities

- Seem to not be listening when spoken to

- Daydream, become easily confused, and move slowly

- Have difficulty processing information as quickly and accurately as others

- Struggle to follow instructions

- Have trouble understanding minute details

A child with ADHD hyperactive-impulsive type has most or all of the following symptoms, excluding situations where these symptoms are better explained by another psychiatric or medical condition:

- Fidget and squirm in their seats

- Talk nonstop

- Dash around, touching or playing with anything and everything in sight

- Have trouble sitting still during dinner, school, doing homework, and story time

- Be constantly in motion

- Have difficulty doing quiet tasks or activities

- Be very impatient

- Blurt out inappropriate comments, show their emotions without restraint, and act without regard for consequences

- Have difficulty waiting for things they want or waiting their turn in games

- Often interrupt conversations or others' activities

Girls tend to have less hyperactivity, inattention, and impulsivity but more intellectual problems. Symptoms of hyperactivity tend to go away with age and turn into "inner restlessness" in teens and adults with ADHD.

People with ADHD of all ages are more likely to have problems with social skills, such as social interaction and forming and maintaining friendships. This is true for all subtypes. About half of children and adolescents with ADHD experience social rejection by their peers compared to 10–15% of non-ADHD children and adolescents. People with attention deficits are prone to having difficulty processing verbal and nonverbal language which can negatively affect social interaction. They also may drift off during conversations, miss social cues, and have trouble learning social skills.

Difficulties managing anger are more common in children with ADHD as are poor handwriting and delays in speech, language and motor development. Although it causes significant impairment, particularly in modern society, many children with ADHD have a good attention span for tasks they find interesting.

Hyperkinetic disorder is a psychiatric neurodevelopmental condition emerging in early childhood that features an enduring pattern of severe, developmentally inappropriate symptoms, namely inattention, hyperactivity, and impulsivity across different settings (e.g., home and school) that significantly impair academic, social and work performance. The disorder, which appears in the World Health Organization's ICD-10, is roughly similiar to the "combined presentation" of attention deficit hyperactivity disorder in the American Psychiatric Association's DSM-V.

Hyperkinetic people display disorganized, poorly controlled and excessive activity; they lack perseverance in tasks involving thought and attention, and tend to move from one activity to the next without completing any. They are frequently accident-prone, reckless and impulsive, and may thoughtlessly (rather than defiantly) break rules. Cognitive impairment and delayed language and motor development are more common in this group than in the general population; and they may experience low self-esteem and engage in dissocial behavior as a consequence of the disorder.

While hyperkinetic children are commonly incautious and unreserved with adults, they might be isolated and unpopular with other children.

A personality development disorder is an inflexible and pervasive pattern of inner experience and behavior in children and adolescents, that markedly deviates from the expectations of the individual's culture. Personality development disorder is not recognized as a mental disorder in any of the medical manuals, such as the ICD-10 or the DSM-IV, neither is it part of the proposed revision of this manual, the DSM-5. DSM-IV allows the diagnosis of personality disorders in children and adolescents only as an exception.

This diagnosis is currently proposed by a few authors in Germany. The term personality "development" disorder is used to emphasize the changes in personality development which might still take place and the open outcome during development. Personality development disorder is considered to be a childhood risk factor or early stage of a later personality disorder in adulthood.

Adults usually show personality patterns over a long duration of time. Children and adolescents however still show marked changes in personality development. Some of these children and adolescents have a hard time developing their personalities in an ordinary way. DSM-IV states, for example, that children and adolescents are at higher risk to develop an antisocial personality disorder if they showed signs of conduct disorder and attention deficit disorder before the age of 10. This led Adam & Breithaupt-Peters (2010) to the idea that these children and adolescents need to be looked at more carefully. The therapy which these children and adolescents need might be more intense and maybe even different from looking at the disorders traditionally. The concept of personality development disorders also focuses on the severity of the disorder and the poor prognosis. An early diagnosis might help to get the right treatment at an early stage and thus might help to prevent a personality disorder outcome in adulthood.

Overall, studies have shown that people with ADHD tend to have lower scores on intelligence quotient (IQ) tests. The significance of this is controversial due to the differences between people with ADHD and the difficulty determining the influence of symptoms, such as distractibility, on lower scores rather than intellectual capacity. In studies of ADHD, higher IQs may be over represented because many studies exclude individuals who have lower IQs despite those with ADHD scoring on average 9 points lower on standardized intelligence measures.

According to Adam und Breithaupt-Peters personality development disorders are defined as complex disorders

- which show similarity to a certain type of personality disorder in adulthood

- which persist over a long period of time (more than a year) and show a tendency towards being chronic

- which have a severe negative impact on more than one important area of functioning or social life

- which show resistance to traditional educational and therapeutic treatment methods

- which result in a reduced insight into or ignorance of the own problem behavior. The family usually suffers more than the child or adolescent and has a hard time dealing with the diminished introspection.

- which make positive interactions between the children/adolescents and other people merely impossible. Instead social collisions are part of everyday life.

- which threaten the social integration of the young person into a social life and might result in an emotional disability.

The likely course and outcome of mental disorders varies and is dependent on numerous factors related to the disorder itself, the individual as a whole, and the social environment. Some disorders are transient, while others may be more chronic in nature.

Even those disorders often considered the most serious and intractable have varied courses i.e. schizophrenia, psychotic disorders, and personality disorders. Long-term international studies of schizophrenia have found that over a half of individuals recover in terms of symptoms, and around a fifth to a third in terms of symptoms and functioning, with some requiring no medication. At the same time, many have serious difficulties and support needs for many years, although "late" recovery is still possible. The World Health Organization concluded that the long-term studies' findings converged with others in "relieving patients, carers and clinicians of the chronicity paradigm which dominated thinking throughout much of the 20th century."

Around half of people initially diagnosed with bipolar disorder achieve syndromal recovery (no longer meeting criteria for the diagnosis) within six weeks, and nearly all achieve it within two years, with nearly half regaining their prior occupational and residential status in that period. However, nearly half go on to experience a new episode of mania or major depression within the next two years. Functioning has been found to vary, being poor during periods of major depression or mania but otherwise fair to good, and possibly superior during periods of hypomania in Bipolar II.

Intermittent explosive disorder (sometimes abbreviated as IED) is a behavioral disorder characterized by explosive outbursts of anger and violence, often to the point of rage, that are disproportionate to the situation at hand (e.g., impulsive screaming triggered by relatively inconsequential events). Impulsive aggression is not premeditated, and is defined by a disproportionate reaction to any provocation, real or perceived. Some individuals have reported affective changes prior to an outburst (e.g., tension, mood changes, energy changes, etc.).

The disorder is currently categorized in the "Diagnostic and Statistical Manual of Mental Disorders" (DSM-5) under the "Disruptive, Impulse-Control, and Conduct Disorders" category. The disorder itself is not easily characterized and often exhibits comorbidity with other mood disorders, particularly bipolar disorder. Individuals diagnosed with IED report their outbursts as being brief (lasting less than an hour), with a variety of bodily symptoms (sweating, stuttering, chest tightness, twitching, palpitations) reported by a third of one sample. Aggressive acts are frequently reported accompanied by a sensation of relief and in some cases pleasure, but often followed by later remorse.

The current DSM-5 criteria for Intermittent Explosive Disorder include:

- Recurrent outbursts that demonstrate an inability to control impulses, including either of the following:

- Verbal aggression (tantrums, verbal arguments or fights) or physical aggression that occurs twice in a week-long period for at least three months and does not lead to destruction of property or physical injury (Criterion A1)

- Three outbursts that involve injury or destruction within a year-long period (Criterion A2)

- Aggressive behavior is grossly disproportionate to the magnitude of the psychosocial stressors (Criterion B)

- The outbursts are not premeditated and serve no premeditated purpose (Criterion C)

- The outbursts cause distress or impairment of functioning, or lead to financial or legal consequences (Criterion D)

- The individual must be at least six years old (Criterion E)

- The recurrent outbursts cannot be explained by another mental disorder and are not the result of another medical disorder or substance use (Criterion F)

It is important to note that DSM-5 now includes two separate criteria for types of aggressive outbursts (A1 and A2) which have empirical support:

- Criterion A1: Episodes of verbal and/or non damaging, nondestructive, or non injurious physical assault that occur, on average, twice weekly for three months. These could include temper tantrums, tirades, verbal arguments/fights, or assault without damage. This criterion includes high frequency/low intensity outbursts.

- Criterion A2: More severe destructive/assaultive episodes which are more infrequent and occur, on average, three times within a twelve-month period. These could be destroying an object without regard to value, assaulting an animal or individual. This criterion includes high-intensity/low-frequency outbursts.

In many ways, those who have an SCT profile have some of the opposite symptoms of those with classic ADHD: instead of being hyperactive, extroverted, obtrusive, excessively energetic and risk takers, those with SCT are drifting, absent-minded, listless, introspective and daydreamy. They feel as if "in the fog" and seem "out of it".

The comorbid psychiatric problems often associated with SCT are more often of the internalizing types, such as anxiety, unhappiness or depression. Most consistent across studies was a pattern of reticence and social withdrawal in interactions with peers. Their typically shy nature and slow response time has often been misinterpreted as aloofness or disinterest by others. In social group interactions, those with SCT may be ignored. People with classic ADHD are more likely to be rejected in these situations, because of their social intrusiveness or aggressive behavior. Compared to children with SCT, they are also much more likely to show antisocial behaviours like substance abuse, oppositional-defiant disorder or conduct disorder (frequent lying, stealing, fighting etc.). Fittingly, in terms of personality, ADHD seems to be associated with sensitivity to reward and fun seeking while SCT may be associated with punishment sensitivity.

Additionally, requirements for a proposed diagnosis such as the number and duration of symptoms and the impact on functioning are continuing to be investigated. But there is no doubt that both ADHD and SCT are found in children and adults and are linked to significant impairment and a diminished quality of life (QoL). The research by Barkley suggests that this is especially true if ADHD and SCT occur together: In adults, those comorbid cases were more likely to be unmarried and to be out of work on disability compared to cases with ADHD alone. But SCT alone is also present in the population and can be quite impairing in educational and occupational settings, even if it is not as pervasively impairing as ADHD.

The definition and classification of mental disorders are key issues for researchers as well as service providers and those who may be diagnosed. For a mental state to classify as a disorder, it generally needs to cause dysfunction. Most international clinical documents use the term mental "disorder", while "illness" is also common. It has been noted that using the term "mental" (i.e., of the mind) is not necessarily meant to imply separateness from brain or body.

According to DSM-IV, a mental disorder is a psychological syndrome or pattern which is associated with distress (e.g. via a painful symptom), disability (impairment in one or more important areas of functioning), increased risk of death, or causes a significant loss of autonomy; however it excludes normal responses such as grief from loss of a loved one, and also excludes deviant behavior for political, religious, or societal reasons not arising from a dysfunction in the individual.

DSM-IV precedes the definition with caveats, stating that, as in the case with many medical terms, "mental disorder" "lacks a consistent operational definition that covers all situations", noting that different levels of abstraction can be used for medical definitions, including pathology, symptomology, deviance from a normal range, or etiology, and that the same is true for mental disorders, so that sometimes one type of definition is appropriate, and sometimes another, depending on the situation.

In 2013, the American Psychiatric Association (APA) redefined mental disorders in the DSM-5 as "a syndrome characterized by clinically significant disturbance in an individual's cognition, emotion regulation, or behavior that reflects a dysfunction in the psychological, biological, or developmental processes underlying mental functioning.”

Emotional and behavioral disorders (EBD; sometimes called emotional disturbance or serious emotional disturbance) refer to a disability classification used in educational settings that allows educational institutions to provide special education and related services to students that have poor social or academic adjustment that cannot be better explained by biological abnormalities or a developmental disability.

The classification is often given to students that need individualized behavior supports to receive a free and appropriate public education, but would not be eligible for an individualized education program under another disability category of the Individuals with Disabilities Education Act (IDEA).

While antisocial personality disorder is a mental disorder diagnosed in adulthood, it has its precedent in childhood. The DSM-5's criteria for ASPD require that the individual have conduct problems evident by the age of 15. Persistent antisocial behavior as well as a lack of regard for others in childhood and adolescence is known as conduct disorder and is the precursor of ASPD. About 25-40% of youths with conduct disorder will be diagnosed with ASPD in adulthood.

Conduct disorder (CD) is a disorder diagnosed in childhood that parallels the characteristics found in ASPD and is characterized by a repetitive and persistent pattern of behavior in which the basic rights of others or major age-appropriate norms are violated. Children with the disorder often display impulsive and aggressive behavior, may be callous and deceitful, and may repeatedly engage in petty crime such as stealing or vandalism or get into fights with other children and adults. This behavior is typically persistent and may be difficult to deter with threat or punishment. Attention deficit hyperactivity disorder (ADHD) is common in this population, and children with the disorder may also engage in substance abuse." CD is differentiated from oppositional defiant disorder (ODD) in that children with ODD do not commit aggressive or antisocial acts against other people, animals, and property, though many children diagnosed with ODD are subsequently rediagnosed with CD.

Two developmental courses for CD have been identified based on the age at which the symptoms become present. The first is known as the "childhood-onset type" and occurs when conduct disorder symptoms are present before the age of 10 years. This course is often linked to a more persistent life course and more pervasive behaviors, and children in this group express greater levels of ADHD symptoms, neuropsychological deficits, more academic problems, increased family dysfunction, and higher likelihood of aggression and violence. The second is known as the "adolescent-onset type" and occurs when conduct disorder develops after the age of 10 years. Compared to the childhood-onset type, less impairment in various cognitive and emotional functions are present, and the adolescent-onset variety may remit by adulthood. In addition to this differentiation, the DSM-5 provides a specifier for a callous and unemotional interpersonal style, which reflects characteristics seen in psychopathy and are believed to be a childhood precursor to this disorder. Compared to the adolescent-onset subtype, the childhood onset subtype, especially if callous and unemotional traits are present, tends to have a worse treatment outcome.

Antisocial personality disorder is defined by a pervasive and persistent disregard for morals, social norms, and the rights and feelings of others. Individuals with this personality disorder will typically have no compunction in exploiting others in harmful ways for their own gain or pleasure and frequently manipulate and deceive other people, achieving this through wit and a facade of superficial charm or through intimidation and violence. They may display , think lowly and negatively of others, and lack remorse for their harmful actions and have a callous attitude to those they have harmed. Irresponsibility is a core characteristic of this disorder: they can have significant difficulties in maintaining stable employment as well as fulfilling their social and financial obligations, and people with this disorder often lead exploitative, unlawful, or parasitic lifestyles.

Those with antisocial personality disorder are often impulsive and reckless, failing to consider or disregarding the consequences of their actions. They may repeatedly disregard and jeopardize their own safety and the safety of others and place themselves and others in danger. They are often aggressive and hostile and display a disregulated temper and can lash out violently with provocation or frustration. Individuals are prone to substance abuse and addiction, and the abuse of various psychoactive substances is common in this population. These behaviors lead such individuals into frequent conflict with the law, and many people with ASPD have extensive histories of antisocial behavior and criminal infractions stemming back before adulthood.

Serious problems with interpersonal relationships are often seen in those with the disorder. Attachments and emotional bonds are weak, and interpersonal relationships often revolve around the manipulation, exploitation, and abuse of others. While they generally have no problems in establishing relationships, they may have difficulties in sustaining and maintaining them. Relationships with family members and relatives are often strained due to their behavior and the frequent problems that these individuals may get into.

The signs and symptoms of impulse-control disorders vary based on the age of the persons suffering from them, the actual type of impulse-control that they are struggling with, the environment in which they are living, and whether they are male, female, or other.

Disorders characterized by impulsivity that were not categorized elsewhere in the DSM-IV-TR were also included in the category "Impulse-control disorders not elsewhere classified". Trichotillomania (hair-pulling) and skin-picking were moved in DSM-5 to the obsessive-compulsive chapter. Additionally, other disorders not specifically listed in this category are often classed as impulsivity disorders. Terminology was changed in the DSM-V from "Not Otherwise Classified" to "Not Elsewhere Classified".

Pediatricians are often the first health professionals to assess and raise suspicions of RAD in children with the disorder. The initial presentation varies according to the child's developmental and chronological age, although it always involves a disturbance in social interaction. Infants up to about 18–24 months "may" present with non-organic failure to thrive and display abnormal responsiveness to stimuli. Laboratory investigations will be unremarkable barring possible findings consistent with malnutrition or dehydration, while serum growth hormone levels will be normal or elevated.

The core feature is severely inappropriate social relating by affected children. This can manifest itself in two ways:

1. Indiscriminate and excessive attempts to receive comfort and affection from any available adult, even relative strangers (older children and adolescents may also aim attempts at peers).

2. Extreme reluctance to initiate or accept comfort and affection, even from familiar adults, especially when distressed.

While RAD is likely to occur in relation to neglectful and abusive treatment, automatic diagnoses on this basis alone cannot be made, as children can form stable attachments and social relationships despite marked abuse and neglect.

The name of the disorder emphasizes problems with attachment but the criteria includes symptoms such as failure to thrive, a lack of developmentally appropriate social responsiveness, apathy, and onset before 8 months.

Reactive attachment disorder (RAD) is described in clinical literature as a severe and relatively uncommon disorder that can affect children. RAD is characterized by markedly disturbed and developmentally inappropriate ways of relating socially in most contexts. It can take the form of a persistent failure to initiate or respond to most social interactions in a developmentally appropriate way—known as the "inhibited form". Due to recent revision in the DSM-5 the "disinhibited form" is now considered a separate diagnosis named "Disinhibited attachment disorder".

RAD arises from a failure to form normal attachments to primary caregivers in early childhood. Such a failure could result from severe early experiences of neglect, abuse, abrupt separation from caregivers between the ages of six months and three years, frequent change of caregivers, or a lack of caregiver responsiveness to a child's communicative efforts. Not all, or even a majority of such experiences, result in the disorder. It is differentiated from pervasive developmental disorder or developmental delay and from possibly comorbid conditions such as intellectual disability, all of which can affect attachment behavior. The criteria for a diagnosis of a reactive attachment "disorder" are very different from the criteria used in assessment or categorization of attachment "styles" such as insecure or disorganized attachment.

Children with RAD are presumed to have grossly disturbed internal working models of relationships that may lead to interpersonal and behavioral difficulties in later life. There are few studies of long-term effects, and there is a lack of clarity about the presentation of the disorder beyond the age of five years. However, the opening of orphanages in Eastern Europe following the end of the Cold War in the early-1990s provided opportunities for research on infants and toddlers brought up in very deprived conditions. Such research broadened the understanding of the prevalence, causes, mechanism and assessment of disorders of attachment and led to efforts from the late-1990s onwards to develop treatment and prevention programs and better methods of assessment. Mainstream theorists in the field have proposed that a broader range of conditions arising from problems with attachment should be defined beyond current classifications.

Mainstream treatment and prevention programs that target RAD and other problematic early attachment behaviors are based on attachment theory and concentrate on increasing the responsiveness and sensitivity of the caregiver, or if that is not possible, placing the child with a different caregiver. Most such strategies are in the process of being evaluated. Mainstream practitioners and theorists have presented significant criticism of the diagnosis and treatment of alleged reactive attachment disorder or the theoretically baseless "attachment disorder" within the controversial form of psychotherapy commonly known as attachment therapy. Attachment therapy has a scientifically unsupported theoretical base and uses diagnostic criteria or symptom lists markedly different to criteria under ICD-10 or DSM-IV-TR, or to attachment behaviors. A range of treatment approaches are used in attachment "therapy", some of which are physically and psychologically coercive, and considered to be to attachment "theory". Many constitute abuse.