The validity of the age-of-onset criterion (AOC), with symptoms emerging before age 7, in the diagnosis of attention deficit/hyperactivity disorder was evaluated by analysis of data from interviews with 9- to 16-year-olds from the Great Smoky Mountains Study, at the University of North Carolina, Chapel Hill, NC. A majority of youths with ADHD were reported to first exhibit symptoms in early childhood and before age 7. Most parents considered symptoms to have “always” been present, without a specific date of onset. The percentage of youths first exhibiting symptoms after age 7 was higher in the inattentive group (26%) than in the hyperactive-impulsive (8%) and combined groups (13%). Patients with early onset inattentive symptoms were at increased risk for comorbid ODD, while those with late-onset inattentive symptoms were at increased risk for comorbid depression. The current AOC results in the underidentification of youths in the inattentive group, late onset type. The continued inclusion of the AOC for the assessment of combined but not the inattentive type of ADHD is supported. Early onset ADHD was associated with worse clinical outcome in youths with the combined subtype but not with the inattentive subtype. 
COMMENT. The recent challenge to the inclusion of an age-of-onset criterion for the diagnosis of ADHD may be valid for patients with the inattentive subtype. The current AOC of less than 7 years may exclude patients in the late onset inattentive group, but it appears to be valid for the assessment of the combined group.