Research has repeatedly shown that hyperactive boys, or those with ADHD, are at increased risk for antisocial activities in adolescence and young adulthood. This is especially so if they also had conduct problems as children or teens. Here we summarize the results and clinical implications of our own study of this issue, showing an increased risk for criminality as adults in children diagnosed as hyperactive. Our study is among the longest in duration (30 years) and was published last year in the Journal of the American Academy of Child and Adolescent Psychiatry (Satterfield et al., 2007). That paper should be consulted for a detailed presentation of our methods, analyses, results, and references. The following article is a summary and adaptation of this earlier paper.