We report a prospective longitudinal study of 101 male adolescents (ages 16 to 23 years) who had been diagnosed hyperactive in childhood (ages 6 to 12 years), compared with 100 normal controls. The DSM-III diagnoses were made blind to group membership. Information was obtained for 98% of the original cohort. The full attention deficit disorder with hyperactivity (ADDH) syndrome persisted in 31% of the probands vs in 3% of the controls. The only other two conditions that distinguished the groups significantly were conduct and substance use disorders. These disorders aggregated significantly among the probands with continued ADDH. The results indicate that the greatest risk factor for the development of antisocial behavior and drug abuse is the maintenance of ADDH symptoms. Substance use disorders followed the onset of conduct disorder in the overwhelming majority of the cases.