The age at onset of attention deficit hyperactivity disorder

Classification systems inevitably reflect the state of science at the time they are formalized (1). In psychiatry, DSM-III revolutionized the field of mental health diagnosis in 1980 by eschewing theoretical explanations in favor of diagnostic reliability. Among the major consequences of this initiative was the flourishing of evidence-based research, leading to an exponential growth of psychiatric literature. Since then, some diagnostic criteria have been put to the test and retained, removed, or reconceptualized. A maximum age at onset as a diagnostic criterion for attention deficit hyperactivity disorder (ADHD) was introduced in DSM-III on the basis of clinical experience. In DSM-IV-TR, this B criterion specifies that "some hyperactive-impulsive or inattentive symptoms that caused impairment were present before age 7 years." Over the intervening years, a number of studies have addressed the utility of criterion B, generally questioning its contribution to the validity of the diagnosis of ADHD (2).