About half of parents of children with ASD notice their child's unusual behaviors by age 18 months, and about four-fifths notice by age 24 months. According to an article, failure to meet any of the following milestones "is an absolute indication to proceed with further evaluations. Delay in referral for such testing may delay early diagnosis and treatment and affect the long-term outcome".

- No babbling by 12 months.

- No gesturing (pointing, waving, etc.) by 12 months.

- No single words by 16 months.

- No two-word (spontaneous, not just echolalic) phrases by 24 months.

- Any loss of any language or social skills, at any age.

The United States Preventive Services Task Force in 2016 found it was unclear if screening was beneficial or harmful among children in whom there is no concerns. The Japanese practice is to screen all children for ASD at 18 and 24 months, using autism-specific formal screening tests. In contrast, in the UK, children whose families or doctors recognize possible signs of autism are screened. It is not known which approach is more effective. Screening tools include the Modified Checklist for Autism in Toddlers (M-CHAT), the Early Screening of Autistic Traits Questionnaire, and the First Year Inventory; initial data on M-CHAT and its predecessor, the Checklist for Autism in Toddlers (CHAT), on children aged 18–30 months suggests that it is best used in a clinical setting and that it has low sensitivity (many false-negatives) but good specificity (few false-positives). It may be more accurate to precede these tests with a broadband screener that does not distinguish ASD from other developmental disorders. Screening tools designed for one culture's norms for behaviors like eye contact may be inappropriate for a different culture. Although genetic screening for autism is generally still impractical, it can be considered in some cases, such as children with neurological symptoms and dysmorphic features.

While infection with rubella during pregnancy causes fewer than 1% of cases of autism, vaccination against rubella can prevent many of those cases.

Parents of children with Asperger syndrome can typically trace differences in their children's development to as early as 30 months of age. Developmental screening during a routine check-up by a general practitioner or pediatrician may identify signs that warrant further investigation. The United States Preventive Services Task Force in 2016 found it was unclear if screening was beneficial or harmful among children in whom there are no concerns.

The diagnosis of AS is complicated by the use of several different screening instruments, including the Asperger Syndrome Diagnostic Scale (ASDS), Autism Spectrum Screening Questionnaire (ASSQ), Childhood Autism Spectrum Test (CAST) (previously called the Childhood Asperger Syndrome Test), Gilliam Asperger's disorder scale (GADS), Krug Asperger's Disorder Index (KADI), and the Autism-spectrum quotient (AQ; with versions for children, adolescents and adults). None have been shown to reliably differentiate between AS and other ASDs.

ASD can be detected as early as 18 months or even younger in some cases. A reliable diagnosis can usually be made by the age of two years. The diverse expressions of ASD symptoms pose diagnostic challenges to clinicians. Individuals with an ASD may present at various times of development (e.g., toddler, child, or adolescent), and symptom expression may vary over the course of development. Furthermore, clinicians must differentiate among pervasive developmental disorders, and may also consider similar conditions, including intellectual disability not associated with a pervasive developmental disorder, specific language disorders, ADHD, anxiety, and psychotic disorders.

Considering the unique challenges in diagnosing ASD, specific practice parameters for its assessment have been published by the American Academy of Neurology, the American Academy of Child and Adolescent Psychiatry, and a consensus panel with representation from various professional societies. The practice parameters outlined by these societies include an initial screening of children by general practitioners (i.e., "Level 1 screening") and for children who fail the initial screening, a comprehensive diagnostic assessment by experienced clinicians (i.e. "Level 2 evaluation"). Furthermore, it has been suggested that assessments of children with suspected ASD be evaluated within a developmental framework, include multiple informants (e.g., parents and teachers) from diverse contexts (e.g., home and school), and employ a multidisciplinary team of professionals (e.g., clinical psychologists, neuropsychologists, and psychiatrists).

After a child shows initial evidence of ASD tendencies, psychologists administer various psychological assessment tools to assess for ASD. Among these measurements, the Autism Diagnostic Interview-Revised (ADI-R) and the Autism Diagnostic Observation Schedule (ADOS) are considered the "gold standards" for assessing autistic children. The ADI-R is a semi-structured parent interview that probes for symptoms of autism by evaluating a child's current behavior and developmental history. The ADOS is a semistructured interactive evaluation of ASD symptoms that is used to measure social and communication abilities by eliciting several opportunities (or "presses") for spontaneous behaviors (e.g., eye contact) in standardized context. Various other questionnaires (e.g., The Childhood Autism Rating Scale, Autism Treatment Evaluation Checklist) and tests of cognitive functioning (e.g., The Peabody Picture Vocabulary Test) are typically included in an ASD assessment battery.

In the UK, there is some diagnostic use of the Diagnostic Interview for Social and Communication Disorders (DISCO) was which was developed for use at The Centre for Social and Communication Disorders, by Lorna Wing and Judith Gould, as both a clinical and a research instrument for use with children and adults of any age. The DISCO is designed to elicit a picture of the whole person through the story of their development and behaviour. In clinical work, the primary purpose is to facilitate understanding of the pattern over time of the specific skills and impairments that underlie the overt behaviour. If no information is available, the clinician has to obtain as much information as possible concerning the details of current skills and pattern of behaviour of the person. This type of dimensional approach to clinical description is useful for prescribing treatment.

Standard diagnostic criteria require impairment in social interaction and repetitive and stereotyped patterns of behavior, activities and interests, without significant delay in language or cognitive development. Unlike the international standard, the DSM-IV-TR criteria also required significant impairment in day-to-day functioning; DSM-5 eliminated AS as a separate diagnosis in 2013, and folded it into the umbrella of autism spectrum disorders. Other sets of diagnostic criteria have been proposed by Szatmari "et al." and by Gillberg and Gillberg.

Diagnosis is most commonly made between the ages of four and eleven. A comprehensive assessment involves a multidisciplinary team that observes across multiple settings, and includes neurological and genetic assessment as well as tests for cognition, psychomotor function, verbal and nonverbal strengths and weaknesses, style of learning, and skills for independent living. The "gold standard" in diagnosing ASDs combines clinical judgment with the Autism Diagnostic Interview-Revised (ADI-R)—a semistructured parent interview—and the Autism Diagnostic Observation Schedule (ADOS)—a conversation and play-based interview with the child. Delayed or mistaken diagnosis can be traumatic for individuals and families; for example, misdiagnosis can lead to medications that worsen behavior.

Underdiagnosis and overdiagnosis may be problems. The cost and difficulty of screening and assessment can delay diagnosis. Conversely, the increasing popularity of drug treatment options and the expansion of benefits has motivated providers to overdiagnose ASD. There are indications AS has been diagnosed more frequently in recent years, partly as a residual diagnosis for children of normal intelligence who are not autistic but have social difficulties.

There are questions about the external validity of the AS diagnosis. That is, it is unclear whether there is a practical benefit in distinguishing AS from HFA and from PDD-NOS; the same child can receive different diagnoses depending on the screening tool. The debate about distinguishing AS from HFA is partly due to a tautological dilemma where disorders are defined based on severity of impairment, so that studies that appear to confirm differences based on severity are to be expected.

There is a division among doctors on the use of the term PDD. Many use the term PDD as a short way of saying PDD-NOS. Others use the general category because the term PDD actually refers to a category of disorders and is not a diagnostic label.

PDD is not itself a diagnosis, while PDD-NOS is a diagnosis. To further complicate the issue, PDD-NOS can also be referred to as "atypical personality development", "atypical PDD", or "atypical Autism".

Because of the "NOS", which means "not otherwise specified", it is hard to describe what PDD-NOS is, other than its being an autism spectrum disorder (ASD). Some people diagnosed with PDD-NOS are close to having Asperger syndrome, but do not quite fit. Others have near full-fledged autism, but without some of its symptoms. The psychology field is considering creating several subclasses within PDD-NOS.

Autism spectrum disorders tend to be highly comorbid with other disorders. Comorbidity may increase with age and may worsen the course of youth with ASDs and make intervention/treatment more difficult. Distinguishing between ASDs and other diagnoses can be challenging, because the traits of ASDs often overlap with symptoms of other disorders, and the characteristics of ASDs make traditional diagnostic procedures difficult.

The most common medical condition occurring in individuals with autism spectrum disorders is seizure disorder or epilepsy, which occurs in 11-39% of individuals with ASD. Tuberous sclerosis, a medical condition in which non-malignant tumors grow in the brain and on other vital organs, occurs in 1-4% of individuals with ASDs.

Intellectual disabilities are some of the most common comorbid disorders with ASDs. Recent estimates suggest that 40-69% of individuals with ASD have some degree of an intellectual disability, more likely to be severe for females. A number of genetic syndromes causing intellectual disability may also be comorbid with ASD, including fragile X syndrome, Down syndrome, Prader-Willi and Angelman syndromes, and Williams syndrome.

Learning disabilities are also highly comorbid in individuals with an ASD. Approximately 25-75% of individuals with an ASD also have some degree of a learning disability.

Various anxiety disorders tend to co-occur with autism spectrum disorders, with overall comorbidity rates of 7-84%. Rates of comorbid depression in individuals with an ASD range from 4–58%. The relationship between ASD and schizophrenia remains a controversial subject under continued investigation, and recent meta-analyses have examined genetic, environmental, infectious, and immune risk factors that may be shared between the two conditions.

Deficits in ASD are often linked to behavior problems, such as difficulties following directions, being cooperative, and doing things on other people's terms. Symptoms similar to those of attention deficit hyperactivity disorder (ADHD) can be part of an ASD diagnosis.

Sensory processing disorder is also comorbid with ASD, with comorbidity rates of 42–88%.

The pervasive developmental disorders are:

- Pervasive developmental disorder not otherwise specified (PDD-NOS), which includes atypical autism, and is the most common (47% of diagnoses);

- Autism, the best-known;

- Asperger syndrome (9% of autism diagnoses);

- Rett syndrome; and

- Childhood disintegrative disorder (CDD).

The first three of these disorders are commonly called the autism spectrum disorders; the last two disorders are much rarer, and are sometimes placed in the autism spectrum and sometimes not.

In May 2013, the "Diagnostic and Statistical Manual-Fifth Edition" ("DSM-5") was released, updating the classification for pervasive developmental disorders. The grouping of disorders, including PDD-NOS, Autism, Asperger Syndrome, Rett Syndrome, and CDD, has been removed and replaced with the general term of Autism Spectrum Disorders. The American Psychiatric Association has concluded that using the general diagnosis of ASD supports more accurate diagnoses. The combination of these disorders was also fueled by the standpoint that Autism is characterized by common symptoms and should therefore bear a single diagnostic term. In order to distinguish between the different disorders, the DSM-5 employs severity levels. The severity levels take into account required support, restricted interests and repetitive behaviors, and deficits in social communication.

Studies suggest that persons with PDD-NOS belong to one of three very different subgroups:

- A high-functioning group (around 25 percent) whose symptoms largely overlap with that of Asperger syndrome, but who differ in terms of having a lag in language development and/or mild cognitive impairment. (The criteria for Asperger syndrome excludes a speech delay or a cognitive impairment.)

- A group (around 25 percent) whose symptoms more closely resemble those of autism spectrum disorder, but do not fully meet all its diagnostic signs and symptoms.

- The biggest group (around 50 percent) consists of those who meet all the diagnostic criteria for autism spectrum disorder, but whose stereotypical and repetitive behaviors are noticeably mild.

PDD-NOS is an old diagnostic category. It is no longer included as an option for an Autism Spectrum Disorder and is not part of the DSM-5, but is included in the ICD-10.

The diagnosis of a pervasive developmental disorder not otherwise specified is given to individuals with difficulties in the areas of social interaction, communication, and/or stereotyped behavior patterns or interests, but who do not meet the full DSM-IV criteria for autism or another PDD. This does not necessarily mean that PDD-NOS is a milder disability than the other PDDs. It only means that individuals who receive this diagnosis do not meet the diagnostic criteria of the other PDDs, but that there is still a pervasive developmental disorder that affects the individual in the areas of communication, socialization and behavior.

As for the other pervasive developmental disorders, diagnosis of PDD-NOS requires the involvement of a team of specialists. The individual needs to undergo a full diagnostic evaluation, including a thorough medical, social, adaptive, motor skills and communication history. Other parts of an assessment can be behavioral rating scales, direct behavioral observations, psychological assessment, educational assessment, communication assessment, and occupational assessment.

Description of PDD-NOS merely as a "subthreshold" category without a more specific case definition poses methodological problems for research regarding the relatively heterogeneous group of people who receive this diagnosis. However, it appears that children with PDD-NOS show fewer intellectual deficits than autistic children, and that they may come to professional attention at a later age.

Cases are typically diagnosed by 35 months of age, much earlier than those of Asperger syndrome. This phenomenon is most likely due to the early delay in speech and language. While there is no single accepted standard diagnostic measure for HFA, one of the most commonly used tools for early detection is the Social Communication Questionnaire. If the results of the test indicate an autism spectrum disorder, a comprehensive evaluation may lead to the diagnosis of HFA. Some characteristics used to diagnose an individual with autism include a lack of eye contact, pointing, and deficits in social interactions. The Autism Diagnostic Interview-Revised and Autism Diagnostic Observation Schedule are two evaluations utilized in the standard diagnosis process.

There are two classifications of different social interaction styles associated with HFA. The first is an active-but-odd social interaction style classified by ADHD symptoms, poor executive functioning, and psychosocial problems. The difficulty controlling impulses could cause the active-but-odd social behaviors present in some children with HFA. The second social interaction type is a passive style. This aloof style is characterized by a lack of social initiations and could possibly be caused by social anxiety.

Treatments for HFA address individual symptoms, rather than the condition as a whole. For instance, to treat anxiety, which is often associated with HFA, the main treatment is cognitive behavior therapy. While this is the tested and approved treatment for anxiety, it does not quite meet the needs associated with the symptoms of HFA. There is very little discussion of the parent's role in anxiety intervention for children and teenagers. A revised version of cognitive behavior therapy has parents and teachers acting in a role as social coaches to help the children or young adults cope with the issues they are facing. There have been several trials proving that the involvement of parents in the lives of the children affected with anxiety associated with HFA is important.

No single intervention exists to aid individuals with high-functioning autism. However, there are proactive strategies, such as self care and self-management, designed to maintain or change behavior to make living with high functioning autism easier. Self-management strategies aim to provide skills necessary to self-regulate behavior, leading to greater levels of independence. Improving self-management skills allows the individual to be more self-reliant rather than having to rely on an external source for supervision or control. Self-monitoring is a framework, not a rigid structure, designed to encourage independence and self-control. Self-monitoring is not for everyone. It requires the attention and dedication of the individual with high-functioning autism as well as the individual overseeing the progress.

A framework for self-monitoring is provided below

- Identify positive target behaviors

- Establish an alternative behavior that is positive/constructive

- Establish a self-recording sheet

- Individuals can make sure to stay on track with intended goals

- Set goals and keep them

The goal of self-monitoring is to enforce self-monitoring independently without prompting.

Loss of language and skills related to social interaction and self-care are serious. The affected children face ongoing disabilities in certain areas and require long term care. Treatment of CDD involves both behavior therapy, environmental therapy and medications.

- Behavior therapy: The main aim of Applied Behavior Analysis (ABA) is to systematically teach the child to relearn language, self-care and social skills. The treatment programs designed in this respect "use a system of rewards to reinforce desirable behaviors and discourage problem behavior." ABA programs may be designed by a board-certified specialist in behavior analysis called a "BCBA" (Board Certified Behavior Analyst), but ABA is also widely used by a number of other health care personnel from different fields like psychologists, speech therapists, physical therapists and occupational therapists with differing levels of expertise. Parents, teachers and caregivers are instructed to use these behavior therapy methods at all times.

- Environmental Therapy: Sensory Enrichment Therapy uses enrichment of the sensory experience to improve symptoms in autism, many of which are common to CDD.

- Medications: There are no medications available to directly treat CDD. Antipsychotic medications are used to treat severe behavior problems like aggressive stance and repetitive behavior patterns. Anticonvulsant medications are used to control seizures.

The childhood disintegrative disorder (CDD), also known as Heller's syndrome and disintegrative psychosis, is a rare condition characterized by late onset of developmental delays—or stunning reversals—in language, social function, and motor skills. Researchers have not been successful in finding a cause for the disorder. CDD has some similarity to autism, and is sometimes considered a low-functioning form of it. In May 2013, the term CDD, along with other types of autism, was fused into a single diagnostic term called "autism spectrum disorder" under the new DSM-5 manual. Therefore, CDD is now also called "regressive autism", being that this term can now refer to any type of autism spectrum disorder that involves regression, including CDD.

CDD was originally described by Austrian educator Theodor Heller (1869–1938) in 1908, 35 years before Leo Kanner and Hans Asperger described autism. Heller had previously used the name "dementia infantilis" for the syndrome.

An apparent period of fairly normal development is often noted before a regression in skills or a series of regressions in skills. The age at which this regression can occur varies, but typically after 3 years of normal development. The regression can be so dramatic that the child may be aware of it, and may in its beginning even ask, vocally, what is happening to them. Some children describe or appear to be reacting to hallucinations, but the most obvious symptom is that skills apparently attained are lost.

Many children are already somewhat delayed when the disorder becomes apparent, but these delays are not always obvious in young children. This has been described by many writers as a devastating condition, affecting both the family and the individual's future. As is the case with all pervasive developmental disorder categories, there is considerable controversy about the right treatment for CDD.

Assessments for developmental coordination disorder typically require a developmental history, detailing ages at which significant developmental milestones, such as crawling and walking, occurred. Motor skills screening includes activities designed to indicate developmental coordination disorder, including balancing, physical sequencing, touch sensitivity, and variations on walking activities.

The American Psychiatric Association has four primary inclusive diagnostic criteria for determining if a child has developmental coordination disorder.

The criteria are as follows:

1. Motor Coordination will be greatly reduced, although the intelligence of the child is normal for the age.

2. The difficulties the child experiences with motor coordination or planning interfere with the child's daily life.

3. The difficulties with coordination are not due to any other medical condition

4. If the child does also experience comorbidities such as mental retardation; motor coordination is still disproportionally affected.

Screening tests which can be used to assess developmental coordination disorder include:-

- Movement Assessment Battery for Children (Movement-ABC – Movement-ABC 2)

- Peabody Developmental Motor Scales- Second Edition (PDMS-2)

- Bruininks-Oseretsky Test of Motor Proficiency (BOTMP-BOT-2)

- Motoriktest für vier- bis sechsjährige Kinder (MOT 4-6)

- Körperkoordinationtest für Kinder (KTK)

- Test of Gross Motor Development, Second Edition (TGMD-2)

- Maastrichtse Motoriek Test (MMT)

- Wechsler Adult Intelligence Scale (WAIS-IV)

- Wechsler Individual Achievement Test (WAIT-II)

- Test of Word Reading Efficiency (TOWRE-2)

- Developmental Coordination Disorder Questionnaire (DCD-Q)

- Children's Self-Perceptions of Adequacy in, and Predilection for Physical Activity (CSAPPA)

Currently there is no single gold standard assessment test.

A baseline motor assessment establishes the starting point for developmental intervention programs. Comparing children to normal rates of development may help to establish areas of significant difficulty.

However, research in the "British Journal of Special Education" has shown that knowledge is severely limited in many who should be trained to recognise and respond to various difficulties, including developmental coordination disorder, dyslexia and deficits in attention, motor control and perception (DAMP). The earlier that difficulties are noted and timely assessments occur, the quicker intervention can begin. A teacher or GP could miss a diagnosis if they are only applying a cursory knowledge.

"Teachers will not be able to recognise or accommodate the child with learning difficulties in class if their knowledge is limited. Similarly GPs will find it difficult to detect and appropriately refer children with learning difficulties."

Once the patient and family have been educated about the nature, management and treatment of the disorder and a decision has been made to treat, the European ADHD Guidelines group recommends medication rather than behavioral training as the first treatment approach; and the UK's National Institute for Health and Clinical Excellence recommends medication as first line treatment for those with hyperkinesis/severe ADHD, and the provision of group parent-training in all cases of ADHD.

Although not necessary for the diagnosis, individuals with intellectual disability are at higher risk for SMD. It is more common in boys, and can occur at any age.

The rate in school age children is thought to be about 1.5%, compared with an estimated 5.3% for ADHD.

Late talker is a term used for exceptionally bright people who experience a delay in the development of speech. Commonalities include usually being boys, delayed speech development, highly educated parents, musically gifted families, puzzle-solving abilities, and lagging social development. Many high-achieving late talkers were notoriously strong willed and noncompliant as children. Late talkers can often be misdiagnosed early on as having severe ("low-functioning") autism spectrum disorder (a category known simply as "autism", prior to the DSM-5), and careful professional evaluation is necessary for differential diagnosis, according to Darold Treffert and other experts. One major difference between late talkers and low-functioning autistic children is that for late talkers, communication skills automatically reach a normal level and the child requires no further special treatment with regards to speech. Outlook for late talkers with or without intervention is generally favorable. However, late language emergence can also be an early or secondary sign of high-functioning autism spectrum disorder / Asperger syndrome, or other developmental disorders, such as attention deficit hyperactivity disorder, intellectual disability, learning disability, social communication disorder, or specific language impairment.

Einstein syndrome, a term coined by the economist Thomas Sowell, is also sometimes used to describe late talkers. The term is named after Albert Einstein (often said to have been a late talker, though with questionable evidence), whom Sowell used as the primary example of a late talker in his work. Sowell also included Edward Teller, Srinivasa Ramanujan, the mathematician Julia Robinson, Richard Feynman, and the pianists Clara Schumann and Arthur Rubinstein to be in the late talkers group. As a toddler, the scientist John Clive Ward showed similar behavioral traits to those described by Sowell, according to a brief sketch of his biography.

Sowell claimed late talkers are often inaccurately categorized as having an autism spectrum disorder (ASD), and that a small subset of late talkers are highly intelligent children with common characteristics concentrated in music, memory, math or the sciences. However, as reported by Simon Baron-Cohen, such characteristics are often found in high-functioning autism / Asperger syndrome.

Considered to be neurologically based, nonverbal learning disorder is characterized by verbal strengths as well as visual-spatial, motor, and social skills difficulties. People with this disorder may not at times comprehend nonverbal cues such as facial expression or tone of voice. Challenges with mathematics and handwriting are common.

While various nonverbal impairments were recognized since early studies in child neurology, there is ongoing debate as to whether/or the extent to which existing conceptions of NLD provide a valid diagnostic framework. As originally presented "nonverbal disabilities" (p. 44) or "disorders of nonverbal learning" (p. 272) was a category encompassing non-linguistic learning problems (Johnson and Myklebust, 1967). "Nonverbal learning disabilities" were further discussed by Myklebust in 1975 as representing a subtype of learning disability with a range of presentations involving "mainly visual cognitive processing," social imperception, a gap between higher verbal ability and lower performance IQ, as well as difficulty with handwriting. Later neuropsychologist Byron Rourke sought to develop consistent criteria with a theory and model of brain functioning that would establish NLD as a distinct syndrome (1989).

Questions remain about how best to frame the perceptual, cognitive and motor issues associated with NLD.

The DSM-5 (Diagnostic and Statistical Manual) and ICD-10 (International Classification of Diseases) do not include NLD as a diagnosis.

Assorted diagnoses have been discussed as sharing symptoms with NLD—these conditions include Right hemisphere brain damage and Developmental Right Hemisphere Syndrome, Developmental Coordination Disorder, Social-Emotional Processing Disorder, Asperger syndrome, Gerstmann syndrome and others.

Labels for specific associated issues include visual-spatial deficit, dyscalculia, dysgraphia, as well as dyspraxia.

In their 1967 book "Learning Disabilities; Educational Principles and Practices", Doris J. Johnson and Helmer R. Myklebust characterize how someone with these kinds of disabilities appears in a classroom: "An example is the child who fails to learn the meaning of the actions of others...We categorize this child as having a deficiency in social perception, meaning that he has an inability which precludes acquiring the significance of basic nonverbal aspects of daily living, though his verbal level of intelligence falls within or above the average." (p. 272). In their chapter "Nonverbal Disorders Of Learning" (p. 272-306) are sections titled "Learning Though Pictures," (274) "Gesture," (281) "Nonverbal Motor Learning," (282) "Body Image," (285) "Spatial Orientation," (290) "Right-Left Orientation," (292) "Social Imperception," (295) "Distractibility, Perseveration, and Disinhibition." (298)

Nonverbal learning disorder (also known as nonverbal learning disability, NLD, or NVLD) is a learning disorder characterized by verbal strengths as well as visual-spatial, motor, and social skills difficulties. It is sometimes confused with Asperger Syndrome or high IQ. Nonverbal learning disorder has never been included in the American Psychiatric Association's "Diagnostic and Statistical Manual of Mental Disorders" or the World Health Organization's "International Classification of Diseases".

Stereotyped movements are common in infants and young children; if the child is not distressed by movements and daily activities are not impaired, diagnosis is not warranted. When stereotyped behaviors cause significant impairment in functioning, an evaluation for stereotypic movement disorder is warranted. There are no specific tests for diagnosing this disorder, although some tests may be ordered to rule out other conditions. SMD may occur with Lesch-Nyhan syndrome, intellectual disability, and fetal alcohol exposure or as a result of amphetamine intoxication.

When diagnosing stereotypic movement disorder, DSM-5 calls for specification of:

- with or without self-injurious behavior;

- association with another known medical condition or environmental factor;

- severity (mild, moderate or severe).

Developmental coordination disorder is a lifelong neurological condition that is more common in males than in females, with a ratio of approximately four males to every female. The exact proportion of people with the disorder is unknown since the disorder can be difficult to detect due to a lack of specific laboratory tests, thus making diagnosis of the condition one of elimination of all other possible causes/diseases. Approximately 5–6% of children are affected by this condition.

Conduct disorder is classified in the fourth edition of "Diagnostic and Statistical Manual of Mental Disorders" (DSM). It is diagnosed based on a prolonged pattern of antisocial behaviour such as serious violation of laws and social norms and rules in people younger than the age of 18. Similar criteria are used in those over the age of 18 for the diagnosis of antisocial personality disorder. No proposed revisions for the main criteria of conduct disorder exist in the "DSM-5"; there is a recommendation by the work group to add an additional specifier for callous and unemotional traits. According to DSM-5 criteria for conduct disorder, there are four categories that could be present in the child's behavior: aggression to people and animals, destruction of property, deceitfulness or theft, and serious violation of rules.

Almost all adolescents who have a substance use disorder have conduct disorder-like traits, but after successful treatment of the substance use disorder, about half of these adolescents no longer display conduct disorder-like symptoms. Therefore, it is important to exclude a substance-induced cause and instead address the substance use disorder prior to making a psychiatric diagnosis of conduct disorder.

Education, and a "watch and wait" strategy, are the only treatment needed for many, and the majority of individuals with tics do not seek treatment; treatment of tic disorders is similar to treatment of Tourette syndrome.