Diagnosing ADHD in Children
ADHD is usually diagnosed when a child is 6-to-12 years of age. Children in this age group are most easily diagnosed because symptoms caused by ADHD become more noticeable in a school setting. It is more difficult to diagnose ADHD in a child younger than age 6 because the symptoms can also occur periodically during normal development.

ADHD is diagnosed by first having a thorough medical exam to rule out other conditions. An evaluation by a physician, psychologist, or child and adolescent psychiatrist uses specific criteria established by the American Psychiatric Association (APA). Observations of a child's behavior documented by parents, classroom teachers, and others who have regular contact with the child are evaluated.

Diagnosing ADHD in Adults
The clinician will perform an evaluation for ADHD which should include a comprehensive clinical interview surveying past and present ADHD symptoms, developmental and medical history, school history, work history, psychiatric history, social adjustment and general day-to-day adaptive functioning.  This comprehensive interview is intended first to identify evidence of core ADD symptoms and then to ensure that the history of these symptoms is both chronic and pervasive. This exam usually requires one or two hours at minimum. Ideally, the interview should rely on several informants, such as a parent or significant other, and survey behavior from multiple settings (i.e., school, work, home). It is also imperative that the clinician attempt to rule in or rule out other psychiatric diagnoses that may better explain presenting symptoms.

Since many adults are long unaware that they may have ADHD, an adult evaluation should also review any available past objective records such as report cards, transcripts or prior testing/evaluation reports. In some cases psychological testing is helpful in treating Adult ADHD. A comprehensive evaluation is needed in diagnosing adult ADHD for three reasons: to establish an accurate diagnosis, to evaluate for the presence of coexisting medical or educationally disabling conditions, and to rule out alternative explanations for behaviors and/or relationship, occupational or academic difficulties.

The cornerstone for the adult diagnosis of ADHD is the Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition (DSM-IV-TR).  ADHD is diagnosed based on three components: