Children with a tic disorder may exhibit the following symptoms:

- overwhelming urge to make movement

- jerking of arms

- clenching of fists

- excessive eye blinking

- shrugging of shoulders

- kicking

- raising eyebrows

- flaring of nostrils

- production of repetitive noises such as grunting, clicking, moaning, snorting, squealing, or throat clearing

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

Disorder of written expression is a type of learning disability in which a person’s writing ability falls substantially below normally expected range based on the individual’s age, educational background, and measured intelligence. Poor writing skills must interfere significantly with academic progress or daily activities that involves written expression (spelling, grammar, handwriting, punctuation, word usage, etc.). This disorder is also generally concurrent with disorders of reading and/or mathematics, as well as disorders related to behavior. Since it is so often associated with other learning disorders and mental problems, it is uncertain whether it can appear by itself. The prevalence of disorder of written expression is estimated to be of a similar frequency to other learning disorders, between 3 - 5%. A diagnosis can be made based on results of several assessments.

Specific causes of this disorder are unknown. The interaction of physical, psychological, and environmental factors is thought to contribute to the disorder of written expression. In neuropsychological and neurobiological research, some studies show evidence that abnormally high testosterone levels and abnormalities in cognitive processes (visual-motor, linguistic, attentional, and memory) are thought to play a role in learning disorder cases. The impact of brain injuries in both children and adults can impair any of these cognitive processes.

ADHD-PI is an attention-concentration deficit that has everything in common with other forms of ADHD except that it has fewer hyperactivity or impulsivity symptoms and has more directed attention fatigue symptoms.

Different countries have used different ways of diagnosing ADHD-PI. In the United Kingdom, diagnosis is based on quite a narrow set of symptoms, and about 0.5–1% of children are thought to have attention or hyperactivity problems.

This is an ill-defined disorder of uncertain nosological validity. The category is included here because of the evidence that children with moderate to severe intellectual disability (IQ below 35) who exhibit major problems in hyperactivity and inattention frequently show stereotyped behaviours; such children tend not to benefit from stimulant drugs (unlike those with an IQ in the normal range) and may exhibit a severe dysphoric reaction (sometimes with psychomotor retardation) when given stimulants; in adolescence the overactivity tends to be replaced by underactivity (a pattern that is not usual in hyperkinetic children with normal intelligence). It is also common for the syndrome to be associated with a variety of developmental delays, either specific or global. The extent to which the behavioural pattern is a function of low IQ or of organic brain damage is not known, neither is it clear whether the disorders in children with mild intellectual disability who show the hyperkinetic syndrome would be better classified here or under F90.- (Hyperkinetic disorders); at present they are included in F90-.

Diagnostic guidelines

Diagnosis depends on the combination of developmentally inappropriate severe overactivity, motor stereotypies, and moderate to severe intellectual disability; all three must be present for the diagnosis. If the diagnostic criteria for F84.0 (childhood autism), F84.1 (atypical autism) or F84.2 (Rett's syndrome) are met, that condition should be diagnosed instead.

The DSM-5 allows for diagnosis of the "predominantly inattentive" presentations of ADHD (code 314.00) if the individual presents six or more (five for adults) of the following symptoms of inattention for at least six months to a point that is disruptive and inappropriate for developmental level:

- Often does not give close attention to details or makes careless mistakes in schoolwork, work, or other activities.

- Often has trouble keeping attention on tasks or play activities.

- Often does not seem to listen when spoken to directly.

- Often does not follow instructions and fails to finish schoolwork, chores, or duties in the workplace (not due to oppositional behavior or failure to understand instructions).

- Often has trouble organizing activities.

- Often avoids, dislikes, or doesn't want to do things that take a lot of mental effort for a long period (such as schoolwork or homework).

- Often loses things needed for tasks and activities (e.g. toys, school assignments, pencils, books, or tools).

- Is often easily distracted.

- Is often forgetful in daily activities.

An ADHD diagnosis is contingent upon the symptoms of impairment presenting themselves in two or more settings (e.g., at school or work and at home). There must also be clear evidence of clinically significant impairment in social, academic, or occupational functioning. Lastly, the symptoms must not occur exclusively during the course of a pervasive developmental disorder, schizophrenia, or other psychotic disorder, and are not better accounted for by another mental disorder (e.g., mood disorder, anxiety disorder, dissociative disorder, personality disorder).

Besides lack of speech, other common behaviors and characteristics displayed by selectively mute people, according to Dr. Elisa Shipon-Blum's findings, include:

- Shyness, social anxiety, fear of social embarrassment, and/or social isolation and withdrawal

- Difficulty maintaining eye contact

- Blank expression and reluctance to smile

- Difficulty expressing feelings, even to family members

- Tendency to worry more than most people of the same age

- Sensitivity to noise and crowds

On the positive side, many people with this condition have:

- Above-average intelligence, perception, or inquisitiveness

- Creativity and a love for art or music

- Empathy and sensitivity to others' thoughts and feelings

- A strong sense of right and wrong

Diogenes syndrome is a disorder that involves hoarding of rubbish and severe self-neglect. In addition, the syndrome is characterized by domestic squalor, syllogomania, social alienation, and refusal of help. It has been shown that the syndrome is caused as a reaction to stress that was experienced by the patient. The time span in which the syndrome develops is undefined, though it is most accurately distinguished as a reaction to stress that occurs late in life.

In most instances, patients were observed to have an abnormal possessiveness and patterns of compilation in a disordered manner. These symptoms suggest damages on the prefrontal areas of the brain, due to its relation to decision making. Although in contrast, there have been some cases where the hoarded objects were arranged in a methodical manner, which may suggest a cause other than brain damage.

Although most patients have been observed to come from homes with poor conditions, and many had been faced with poverty for a long period of time, these similarities are not considered as a definite cause to the syndrome. Research showed that some of the participants with the condition had solid family backgrounds as well successful professional lives. Half of the patients were of higher intelligence level. This indicates the "Diogenes syndrome" does not exclusively affect those experiencing poverty or those who had traumatic childhood experiences.

The severe neglect that they bring on themselves usually results in physical collapse or mental breakdown. Most individuals who suffer from the syndrome do not get identified until they face this stage of collapse, due to their predilection to refuse help from others.

The patients are generally highly intelligent, and the personality traits that can be seen frequently in patients diagnosed with Diogenes syndrome are aggressiveness, stubbornness, suspicion of others, unpredictable mood swings, emotional instability and deformed perception of reality. Secondary DS is related to mental disorders. The direct relation of the patients' personalities to the syndrome is unclear, though the similarities in character suggest potential avenues for investigation.

Emotional dysregulation in children can be associated with externalizing behaviors including

- exhibiting more extreme emotions

- difficulty identifying emotional cues

- difficulty recognizing their own emotions

- focusing on the negative

- difficulty controlling their attention

- being impulsive

- difficulty decreasing their negative emotions

- difficulty calming down when upset

Emotional dysregulation in children can be associated with internalizing behaviors including

- exhibiting emotions too intense for a situation

- difficulty calming down when upset

- difficulty decreasing negative emotions

- being less able to calm themselves

- difficulty understanding emotional experiences

- becoming avoidant or aggressive when dealing with negative emotions

- experiencing more negative emotions

Diogenes syndrome, also known as senile squalor syndrome, is a disorder characterized by extreme self-neglect, domestic squalor, social withdrawal, apathy, compulsive hoarding of garbage or animals, and lack of shame. Sufferers may also display symptoms of catatonia.

The condition was first recognized in 1966 and designated Diogenes syndrome by Clark et al. The name derives from Diogenes of Sinope, an ancient Greek philosopher, a Cynic and an ultimate minimalist, who allegedly lived in a large jar in Athens. Not only did he not hoard, but he actually sought human company by venturing daily to the Agora. Therefore, this eponym is considered to be a misnomer, but he is actually a representative existence of self-neglect. Other possible terms are "senile breakdown", "Plyushkin's Syndrome" (after a character from Gogol's novel "Dead Souls"), "social breakdown" and "senile squalor syndrome". Frontal lobe impairment may play a part in the causation (Orrell et al., 1989).

Overactive disorder associated with mental retardation and stereotyped movements is a pervasive developmental disorder (PDD) listed in Chapter V(F) of the tenth revision of the International Statistical Classification of Diseases and Related Health Problems (ICD-10); its diagnostic code is F84.4.

Children and adults with selective mutism are fully capable of speech and understanding language but fail to speak in certain situations, though speech is expected of them. The behaviour may be perceived as shyness or rudeness by others. A child with selective mutism may be completely silent at school for years but speak quite freely or even excessively at home. There is a hierarchical variation among people with this disorder: some people participate fully in activities and appear social but do not speak, others will speak only to peers but not to adults, others will speak to adults when asked questions requiring short answers but never to peers, and still others speak to no one and participate in few, if any, activities presented to them. In a severe form known as "progressive mutism", the disorder progresses until the person with this condition no longer speaks to anyone in any situation, even close family members.

Selective mutism is by definition characterized by the following:

- Consistent failure to speak in specific social situations (in which there is an expectation for speaking, e.g., at school) despite speaking in other situations.

- The disturbance interferes with educational or occupational achievement or with social communication.

- The duration of the disturbance is at least 1 month (not limited to the first month of school).

- The failure to speak is not due to a lack of knowledge of, or comfort with, the spoken language required in the social situation.

- The disturbance is not better accounted for by a communication disorder (e.g., childhood-onset fluency disorder) and does not occur exclusively during the course of autism spectrum disorder, schizophrenia, or another psychotic disorder.

Selective mutism is strongly associated with other anxiety disorders, particularly social anxiety disorder. In fact, the majority of children diagnosed with selective mutism also have social anxiety disorder (100% of participants in two studies and 97% in another). Some researchers therefore speculate that selective mutism may be an avoidance strategy used by a subgroup of children with social anxiety disorder to reduce their distress in social situations.

Particularly in young children, SM can sometimes be confused with an autism spectrum disorder, especially if the child acts particularly withdrawn around his or her diagnostician, which can lead to incorrect treatment. Although autistic people may also be selectively mute, they often display other behaviors—hand flapping, repetitive behaviors, social isolation even among family members (not always answering to name, for example)—that set them apart from a child with selective mutism. Some autistic people may be selectively mute due to anxiety in social situations that they do not fully understand. If mutism is entirely due to autism spectrum disorder, it cannot be diagnosed as selective mutism as stated in the last item on the list above.

The former name "elective mutism" indicates a widespread misconception among psychologists that selective mute people choose to be silent in certain situations, while the truth is that they often wish to speak but have difficulty doing so. To reflect the involuntary nature of this disorder, the name was changed to "selective mutism" in 1994.

The incidence of selective mutism is not certain. Due to the poor understanding of this condition by the general public, many cases are likely undiagnosed. Based on the number of reported cases, the figure is commonly estimated to be 1 in 1000, 0.1%. However, a 2002 study in "The Journal of the American Academy of Child and Adolescent Psychiatry" estimated the incidence to be 0.71%.

Neurodevelopmental disorders are impairments of the growth and development of the brain or central nervous system. A narrower use of the term refers to a disorder of brain function that affects emotion, learning ability, self-control and memory and that unfolds as an individual develops and grows.

The term is sometimes erroneously used as an exclusive synonym for autism spectrum disorders.

Delirium develops rapidly over a short period of time and is characterized by a disturbance in cognition, manifested by confusion, excitement, disorientation, and a clouding of consciousness. Hallucinations and illusions are common, and some individuals may experience acute onset change of consciousness. It is a disorder that makes situational awareness and processing new information very difficult for those diagnosed. It usually has a high rate of onset ranging from minutes to hours and sometimes days, but it does not last for very long, only a few hours to weeks. Delirium can also be accompanied by a shift in attention, mood swings, violent or unordinary behaviors, and hallucinations. It can be caused by a preexisting medical condition. Delirium during a hospital stay can result in a longer stay and more risk of complications and long terms stays.

Disorders considered in origin include:

1. Intellectual disability (ID) or intellectual and developmental disability (IDD), previously called mental retardation

2. Autism spectrum disorders, such as Asperger's syndrome or Kanner syndrome

3. Motor disorders including developmental coordination disorder and stereotypic movement disorder Tic disorders including Tourette's syndrome

4. Traumatic brain injury (including congenital injuries such as those that cause cerebral palsy)

5. Communication, speech and language disorders

6. genetic disorders, such as fragile-X syndrome, Down syndrome, attention deficit hyperactivity disorder, schizophrenia, schizotypal disorder, hypogonadotropic hypogonadal syndromes

7. disorders due to neurotoxicants like fetal alcohol spectrum disorder, Minamata disease caused by mercury, behavioral disorders including conduct disorder etc caused by other heavy metals, such as lead, chromium, platinum etc, hydrocarbons like dioxin, PBDEs and PCBs, medications and illegal drugs, like cocaine and others.

Mild and major neurocognitive disorders are usually associated with but not restricted to the elderly. Unlike delirium, conditions under these disorders develop slowly and are characterized by memory loss. In addition to memory loss and cognitive impairment, other symptoms include aphasia, apraxia, agnosia, loss of abstract thought, behavioral/personality changes, and impaired judgment. There may also be behavioral disturbances including psychosis, mood, and agitation.

Mild and major neurocognitive disorders are differentiated based on the severity of their symptoms. Previously known as dementia, major neurocognitive disorder is characterized by significant cognitive decline and interference with independence, while mild neurocognitive disorder is characterized by moderate cognitive decline and does not interfere with independence. To be diagnosed, it must not be due to delirium or other mental disorder. They are also usually accompanied by another cognitive dysfunction. For non-reversible causes of dementia such as age, the slow decline of memory and cognition is lifelong. It can be diagnosed by screening tests such as the Mini Mental State Examination (MMSE).

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.

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.

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.

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.

Previously, the DSM-IV differentiated among three types:

- Factitious disorders with predominantly psychological signs and symptoms: if psychological signs and symptoms predominate in the clinical presentation

- Factitious disorders with predominantly physical signs and symptoms: if physical signs and symptoms predominate in the clinical presentation

- Factitious disorders with combined psychological and physical signs and symptoms: if both psychological and physical signs and symptoms are present and neither predominates in the clinical presentation

Ganser syndrome was once considered a separate factitious disorder. It is a disorder of extreme stress or an organic condition. The patient suffers from approximation or giving absurd answers to simple questions. The syndrome is sometimes diagnosed as merely malingering—however, it is more often defined as a factitious disorder. This has been seen in prisoners following solitary confinement, and the symptoms are consistent in different prisons, though the patients do not know one another.

Symptoms include a clouding of consciousness, somatic conversion symptoms, confusion, stress, loss of personal identity, echolalia, and echopraxia. Individuals also give approximate answers to simple questions such as, "How many legs on a cat?" "Three"; "What's the day after Wednesday?" "Friday"; and so on. The disorder is extraordinarily rare with fewer than 100 recorded cases. While individuals of all backgrounds have been reported with the disorder, there is a higher inclination towards males (75% or more). The average age of those with Ganser syndrome is 32, though it stretches from ages 15–62 years old.

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.