The aim of the study was to test the mediator role of impulsivity, sensation seeking, and proactive and reactive aggression on the relationship between childhood Attention Deficit/Hyperactivity Disorder (ADHD) symptoms and antisocial behavior in a sample of 729 Italian high school students. Although significant mediation effects were observed for impulsivity and sensation seeking, a complete mediation effect was observed only for proactive aggression. The results of this study confirm and extend previous findings suggesting that selected personality traits may represent risk factors for developing antisocial behavior in adolescence/adulthood in subjects with a history of ADHD.