Background: Hyperactive/ADHD children are believed to be a greater risk for adolescent and young adult antisocial activity and drug use/abuse, particularly that subset having comorbid conduct problems/disorder. Method: We report on the lifetime antisocial activities and illegal drug use self-reported at young adult follow-up (mean age 20-21 years; 13+ year follow-up) for a large sample of hyperactive (H; N = 147) and community control (CC; N = 73) children. Parent reports of childhood hyperactivity and conduct problems at study entry, parent and self-reports of ADHD and conduct disorder at adolescence, and parent reports of ADHD at young adulthood are examined for their contribution to antisocial behavior and drug use at adulthood. Results: More of the H group committed a variety of antisocial acts and had been arrested for doing so (corroborated through official arrest records) than did the CC group. The H group also committed a higher frequency of property theft, disorderly conduct, assault with fists, carrying a concealed weapon, and illegal drug possession, as well as more arrests. These activities reduced to two dimensions corresponding to predatory-overt and drug-related antisocial conduct. The H group differed from the CC group only on the latter dimension. Childhood, adolescent, and adult ADHD predicted higher drug-related activities, as did childhood conduct problems. The H group with conduct disorder (CD) reported greater use of most substances than did the H only or CC groups, who did not differ from each other. Severity of teen ADHD and especially lifetime CD predicted use of hard drugs while just lifetime CD predicted marijuana/LSD use. Teen drug use seemed to potentiate increased drug-related antisocial activities beyond the contribution made by teen CD. Conclusions: Hyperactive children are at greater risk for antisocial activities and arrests by young adulthood that appear to be principally associated with illegal drug possession, use, and sale. The having CD, however, appear to engage in greater and more diverse substance use.