This study examines the relation between proactive and reactive antisocial behavior with Attention-Deficit/Hyperactivity Disorder (ADHD) symptoms. Caregivers of children aged 8 to 15 (n = 84) being evaluated at a child psychiatry outpatient clinic served as participants. Given the conceptual similarity between reactive antisocial behavior (ASB) and particular ADHD symptoms, we hypothesized that ADHD symptoms would be more closely related to reactive than to proactive ASB. Based on peer deviancy training models of ASB, we also hypothesized that the relation between ADHD symptoms and proactive ASB would increase from middle childhood to adolescence. Both hypotheses were supported. These findings suggest that reactive ASB is relatively specific to ADHD symptoms, and that intervening before early adolescence may be critical to prevent the onset of comorbid proactive ASB. (Contains 2 tables.)