An analysis of the DSM-IV field trials revealed differences in ages at onset according to ADHD subtype, with the inattentive group exhibiting a later onset (3). The authors of this report also questioned the criterion's diagnostic utility, as its adoption increased false negatives in comparison with clinical validation diagnosis (clinicians validated 75% of cases meeting symptom criteria but lacking the onset criterion). Data from an adult population survey showed that only 50% of individuals with clinical features of ADHD retrospectively recalled an onset before age 7; by contrast, 95% recalled an onset before age 12 and 99% before age 16 (4). A series of studies examining later-onset ADHD cases found that individuals who did not meet the onset criterion resembled those with the full diagnosis in terms of neuropsychological profile, comorbidity, substance use, personality traits, and impairment (5—8). Response to treatment with stimulants has also been shown to be similar among children, adolescents, and adults whether or not they met criterion B (9, 10). Cohort studies, which are unbiased by memory recall, have confirmed the similarities between early- and late-onset ADHD groups in terms of psychopathology and impairment (11—13). For example, in a representative sample of the British population prospectively assessed for ADHD, those with symptoms before age 7 years and those with a new onset of symptoms between ages 7 and 12 years did not differ significantly on clinical, cognitive, and impairment measures or in environmental stressors or perinatal risk factors (G. Polanczyk et al., personal communication, 2009). Prospective data also demonstrate the poor stability of the recall of age at onset, with nearly one-half of the children assessed and diagnosed with ADHD not meeting the onset criterion in later life when reassessed retrospectively (12). In contrast, no studies provided significant findings differentiating children with onset before and after age 7 years.