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.

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.

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.

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.

In children, ADHD occurs with other disorders about ⅔ of the time. Some commonly associated conditions include:

- Learning disabilities have been found to occur in about 20–30% of children with ADHD. Learning disabilities can include developmental speech and language disorders and academic skills disorders. ADHD, however, is not considered a learning disability, but it very frequently causes academic difficulties.

- Tourette syndrome has been found to occur more commonly in the ADHD population.

- Oppositional defiant disorder (ODD) and conduct disorder (CD), which occur with ADHD in about 50% and 20% of cases respectively. They are characterized by antisocial behaviors such as stubbornness, aggression, frequent temper tantrums, deceitfulness, lying, and stealing. About half of those with hyperactivity and ODD or CD develop antisocial personality disorder in adulthood. Brain imaging supports that conduct disorder and ADHD are separate conditions.

- Primary disorder of vigilance, which is characterized by poor attention and concentration, as well as difficulties staying awake. These children tend to fidget, yawn and stretch and appear to be hyperactive in order to remain alert and active.

- Sluggish cognitive tempo (SCT) is a cluster of symptoms that potentially comprises another attention disorder. It may occur in 30–50% of ADHD cases, regardless of the subtype.

- Mood disorders (especially bipolar disorder and major depressive disorder). Boys diagnosed with the combined ADHD subtype are more likely to have a mood disorder. Adults with ADHD sometimes also have bipolar disorder, which requires careful assessment to accurately diagnose and treat both conditions.

- Anxiety disorders have been found to occur more commonly in the ADHD population.

- Obsessive-compulsive disorder (OCD) can co-occur with ADHD and shares many of its characteristics.

- Substance use disorders. Adolescents and adults with ADHD are at increased risk of substance abuse. This is most commonly seen with alcohol or cannabis. The reason for this may be an altered reward pathway in the brains of ADHD individuals. This makes the evaluation and treatment of ADHD more difficult, with serious substance misuse problems usually treated first due to their greater risks.

- Restless legs syndrome has been found to be more common in those with ADHD and is often due to iron deficiency anaemia. However, restless legs can simply be a part of ADHD and requires careful assessment to differentiate between the two disorders.

- Sleep disorders and ADHD commonly co-exist. They can also occur as a side effect of medications used to treat ADHD. In children with ADHD, insomnia is the most common sleep disorder with behavioral therapy the preferred treatment. Problems with sleep initiation are common among individuals with ADHD but often they will be deep sleepers and have significant difficulty getting up in the morning. Melatonin is sometimes used in children who have sleep onset insomnia.

- People with ADHD have an increased risk of persistent bed wetting.

- A 2016 systematic review found a well established association between ADHD and obesity, asthma and sleep disorders, and tentative evidence for association with celiac disease and migraine, while another 2016 systematic review did not support a clear link between celiac disease and ADHD, and stated that routine screening for celiac disease in people with ADHD is discouraged.

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.

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.

Behaviors that are apparent in those with internalizing disorders include depression, withdrawal, anxiety, and loneliness. There are also behavioral characteristics involved with internalizing disorders. Some behavioral abnormalities include poor self-esteem, suicidal behaviors, decreased academic progress, and social withdrawal. Internalizing one's problems, like sadness, can cause the problems to grow into larger burdens such as social withdrawal, suicidal behaviors or thoughts, and other unexplained physical symptoms.

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 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).

The internalizing disorders, with high levels of negative affectivity, include depressive disorders, anxiety disorders, obsessive-compulsive and related disorders, trauma and stressor-related disorders, and dissociative disorders. Others like bulimia, and anorexia also come under this category.

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.

Impulse-control disorder (ICD) is a class of psychiatric disorders characterized by impulsivity – failure to resist a temptation, an urge or an impulse. Many psychiatric disorders feature impulsivity, including substance-related disorders, behavioral addictions, attention deficit hyperactivity disorder, antisocial personality disorder, borderline personality disorder, conduct disorder and some mood disorders.

The fifth edition of the American Psychiatric Association's "Diagnostic and statistical manual of mental disorders" (DSM-5) that was published in 2013 includes a new chapter (not in DSM-IV-TR) on Disruptive, Impulse-Control, and Conduct Disorders covering disorders "characterized by problems in emotional and behavioral self-control".

Five behavioral stages characterize impulsivity: an impulse, growing tension, pleasure on acting, relief from the urge and finally guilt (which may or may not arise).

Whereas vanity involves a quest to aggrandize the appearance, BDD is experienced as a quest to merely normalize the appearance. Although delusional in about one of three cases, the appearance concern is usually nondelusional, an overvalued idea.

The bodily area of focus can be nearly any, yet is commonly face, hair, stomach, thighs, or hips. Some half dozen areas can be a roughly simultaneous focus. Many seek dermatological treatment or cosmetic surgery, which typically do not resolve the distress. On the other hand, attempts at self-treatment, as by skin picking, can create lesions where none previously existed.

BDD shares features with obsessive-compulsive disorder, but involves more depression and social avoidance. BDD often associates with social anxiety disorder. Some experience delusions that others are covertly pointing out their flaws. Cognitive testing and neuroimaging suggest both a bias toward detailed visual analysis and a tendency toward emotional hyperarousal.

Most generally, one experiencing BDD ruminates over the perceived bodily defect up to several hours daily, uses either social avoidance or camouflaging with cosmetics or apparel, repetitively checks the appearance, compares it to that of other persons, and might often seek verbal reassurances. One might sometimes avoid mirrors, repetitively change outfits, groom excessively, or restrict eating.

BDD's severity can wax and wane, and flareups tend to yield absences from school, work, or socializing, sometimes leading to protracted social isolation, with some becoming housebound for extended periods. Social impairment is usually greatest, sometimes approaching avoidance of all social activities. Poor concentration and motivation impair academic and occupational performance. The distress of BDD tends to exceed that of either major depressive disorder or type-2 diabetes, and rates of suicidal ideation and attempts are especially high.

It is common for individuals with PDD-NOS to have more intact social skills and a lower level of intellectual deficit than individuals with other PDDs. Characteristics of many individuals with PDD-NOS are:

- Communication difficulties (e.g., using and understanding language)

- Difficulty with social behavior

- Difficulty with changes in routines or environments

- Uneven skill development (strengths in some areas and delays in others)

- Unusual play with toys and other objects

- Repetitive body movements or behavior patterns

- Preoccupation with fantasy, such as imaginary friends in childhood

Separation anxiety disorder

- excessive stress when separated from home or family

- fear of being alone

- refusal to sleep alone

- clinginess

- excessive worry about safety

- excessive worry about getting lost

- frequent medical complaints with no cause

- refusal to go to school

Selective mutism

- unable to speak in certain social situations, even though they are comfortable speaking at home or with friends

- difficulty maintaining eye contact

- may have blank facial expressions

- stiff body movements

- may have a worrisome personality

- may be incredibly sensitive to sound

- difficulty with verbal and non-verbal expression

- may appear shy, when in reality, they have a fear of people.

Reactive attachment disorder of infancy or early childhood

- withdrawing from others

- aggressive attitude towards peers

- awkwardness or discomfort

- watching others but not engaging in social interaction

Stereotypic movement disorder

- head banging

- nail biting

- hitting or biting oneself

- hand waving or shaking

- rocking back and forth

Estimates of prevalence and gender distribution have varied widely via discrepancies in diagnosis and reporting. In American psychiatry, BDD gained diagnostic criteria in the "DSM-IV", but clinicians' knowledge of it, especially among general practitioners, is constricted. Meanwhile, shame about having the bodily concern, and fear of the stigma of vanity, makes many hide even having the concern.

Via shared symptoms, BDD is commonly misdiagnosed as social-anxiety disorder, obsessive-compulsive disorder, major depressive disorder, or social phobia. Correct diagnosis can depend on specialized questioning and correlation with emotional distress or social dysfunction. Estimates place the Body Dysmorphic Disorder Questionnaire's sensitivity at 100% (0% false negatives) and specificity at 92.5% (7.5% false positives).

Mental retardation is coded on Axis II of the DSM-IV-TR. The diagnostic criteria necessary in order to diagnose intellectual disability consists of:

There are varying degrees of intellectual disability, which are identified by an IQ test.

Mental retardation, Severity Unspecified: This unspecified diagnosis is given when there is a strong assumption that the child is mentally retarded, but cannot be tested because the individual is too impaired, not willing to take the IQ test or is an infant.

Personality disorders (PD) are a class of mental disorders characterized by enduring maladaptive patterns of behavior, cognition, and inner experience, exhibited across many contexts and deviating markedly from those accepted by the individual's culture. These patterns develop early, are inflexible, and are associated with significant distress or disability. The definitions may vary somewhat, according to source. Official criteria for diagnosing personality disorders are listed in the "Diagnostic and Statistical Manual of Mental Disorders" (DSM) and the of the "International Classification of Diseases" (ICD). The DSM-5 lists personality disorders in the same way as other mental disorders, rather than on a separate 'axis', as previously.

Personality, defined psychologically, is the set of enduring behavioral and mental traits that distinguish between individual humans. Hence, personality disorders are defined by experiences and behaviors that differ from societal norms and expectations. Those diagnosed with a personality disorder may experience difficulties in cognition, emotiveness, interpersonal functioning, or impulse control. In general, personality disorders are diagnosed in 40–60% of psychiatric patients, making them the most frequent of psychiatric diagnoses.

Personality disorders are characterized by an enduring collection of behavioral patterns often associated with considerable personal, social, and occupational disruption. Personality disorders are also inflexible and pervasive across many situations, largely due to the fact that such behavior may be ego-syntonic (i.e. the patterns are consistent with the ego integrity of the individual) and are therefore perceived to be appropriate by that individual. This behavior can result in maladaptive coping skills and may lead to personal problems that induce extreme anxiety, distress, or depression. These behaviour patterns are typically recognized in adolescence, the beginning of adulthood or sometimes even childhood and often have a pervasive negative impact on the quality of life.

Many issues occur with classifying a personality disorder. Because the theory and diagnosis of personality disorders occur within prevailing cultural expectations, their validity is contested by some experts on the basis of inevitable subjectivity. They argue that the theory and diagnosis of personality disorders are based strictly on social, or even sociopolitical and economic considerations.

Both diagnostic systems provide a definition and six criteria for a general personality disorder. These criteria should be met by all personality disorder cases before a more specific diagnosis can be made.

The ICD-10 lists these general guideline criteria:

- Markedly disharmonious attitudes and behavior, generally involving several areas of functioning; e.g. affectivity, arousal, impulse control, ways of perceiving and thinking, and style of relating to others;

- The abnormal behavior pattern is enduring, of long standing, and not limited to episodes of mental illness;

- The abnormal behavior pattern is pervasive and clearly maladaptive to a broad range of personal and social situations;

- The above manifestations always appear during childhood or adolescence and continue into adulthood;

- The disorder leads to considerable personal distress but this may only become apparent late in its course;

- The disorder is usually, but not invariably, associated with significant problems in occupational and social performance.

The ICD adds: "For different cultures it may be necessary to develop specific sets of criteria with regard to social norms, rules and obligations."

In DSM-5, any personality disorder diagnosis must meet the following criteria:

- An enduring pattern of inner experience and behavior that deviates markedly from the expectations of the individual’s culture. This pattern is manifested in two (or more) of the following areas:

1. Cognition (i.e., ways of perceiving and interpreting self, other people, and events).

2. Affectivity (i.e., the range, intensity, lability, and appropriateness of emotional response).

3. Interpersonal functioning.

4. Impulse control.

- The enduring pattern is inflexible and pervasive across a broad range of personal and social situations.

- The enduring pattern leads to clinically significant distress or impairment in social, occupational, or other important areas of functioning.

- The pattern is stable and of long duration, and its onset can be traced back at least to adolescence or early adulthood.

- The enduring pattern is not better explained as a manifestation or consequence of another mental disorder.

- The enduring pattern is not attributable to the physiological effects of a substance (e.g., a drug of abuse, a medication) or another medical condition (e.g., head trauma).

Somatic symptom disorders are a group of disorders, all of which fit the definition of physical symptoms similar to those observed in physical disease or injury for which there is no identifiable physical cause. As such, they are a diagnosis of exclusion. Somatic symptoms may be generalized in four major medical categories: neurological, cardiac, pain, and gastrointestinal somatic symptoms.

Symptoms of PDD may include behavioral and communication problems such as:

- Difficulty using and understanding language.

- Difficulty relating to people, objects, and events; for example, lack of eye contact, pointing behavior, and lack of facial responses.

- Unusual play with toys and other objects.

- Difficulty with changes in routine or familiar surroundings.

- Repetitive body movements or behavior patterns, such as hand flapping, hair twirling, foot tapping, or more complex movements.

- Inability to cuddle or be comforted.

- Difficulty regulating behaviors and emotions, which may result in temper tantrums, anxiety, and aggression.

- Emotional breakdowns.

A pervasive developmental disorder not otherwise specified (PDD-NOS) is one of the four autism spectrum disorders (ASD) and also one of the five disorders classified as a pervasive developmental disorder (PDD). According to the DSM-IV, PDD-NOS is a diagnosis that is used for "severe and pervasive impairment in the development of reciprocal social interaction or verbal and nonverbal communication skills, or when stereotyped behavior, interests, and activities are present, but the criteria are not met for a specific PDD" or for several other disorders. PDD-NOS is often called atypical autism, because the criteria for autistic disorder are not met, for instance because of late age of onset, atypical symptomatology, or subthreshold symptomatology, or all of these. Even though PDD-NOS is considered milder than typical autism, this is not always true. While some characteristics may be milder, others may be more severe.

CBD is frequently comorbid with mood, anxiety, substance abuse and eating disorders. People who score highly on compulsive buying scales tend to understand their feelings poorly and have low tolerance for unpleasant psychological states such as bad moods. Onset of CBD occurs in the late teens and early twenties and is generally chronic. CBD is similar to, but distinguished from, OCD hoarding and mania. Compulsive buying is not limited to people who spend beyond their means; it also includes people who spend an inordinate amount of time shopping or who chronically think about buying things but never purchase them. Promising treatments for CBD include medication such as selective serotonin reuptake inhibitors (SSRIs), and support groups such as Debtors Anonymous.