One hundred six clinic-referred boys meeting criteria for DSM-III-R attention-deficit hyperactivity disorder (ADHD) (mean age 9.4 years) were assessed annually for 4 years using structured interviews of multiple informants. Hyperactivity-impulsivity symptoms declined with increasing age, but inattention symptoms did not. Rather, inattention declined only from the first to the second assessment and remained stable thereafter in boys of all ages. The rate of decline in hyperactivity-impulsivity symptoms was independent of the amount and type of treatment received. Boys who still met criteria for ADHD in Years 3 and 4 were significantly younger, more hyperactive-impulsive, and more likely to exhibit conduct disorder in Year 1 than boys who no longer met criteria in Years 3 and 4.