California official arrest records were obtained on 91 percent of the subjects. The hyperactive subjects had significantly higher arrest, conviction, and incarceration rates compared with the control subjects. Childhood antisocial behaviors, socioeconomic status, and IQ predicted adult criminality. Multimodality (MMT) treated boys with attention deficit/hyperactivity disorder (ADHD) did not fare better than drug-treated-only boys with ADHD. The authors conclude that ADHD boys with conduct problems are at increased risk for adult criminality. On the other hand, hyperactive boys without childhood conduct problems are not at increased risk for later criminality. An intensive 3-year MMT treatment of 6-12 year-old hyperactive boys is insufficient to prevent later adult criminality. Treatment given to the MMT group included parent training, individual or group therapy for the child and/or the parents, family therapy, and educational therapy. Control subjects were White boys between 6 and 12 years old selected from public schools. They were matched to the hyperactive boys with conduct problem for age, sex, and as closely as possible for WISC full-scale IQ. 3 tables, 2 figures, and 35 references