Investigating different types of aggression is important to facilitate a better understanding of excessive maladaptive aggression in referred youth. Using regression analysis, the authors investigated demographic, historical, diagnostic, and treatment correlates of proactive aggression and reactive aggression in a heterogeneous population (N = 323) of psychiatrically referred youths. Ratings of proactive and reactive aggression significantly correlated with more established measures of aggression. Results suggest the importance of hyperactive/impulsive behavior, disruptive behavior disorders, and self-reported hostility in youths with both reactive and proactive aggression. Substance use disorders, a family history of substance abuse, and family violence were specifically associated with proactive aggression. Younger age and a history of abuse were correlated with reactive aggression. Implications for clinical interventions and future research are discussed.