The current study examined whether reactive and/or proactive aggression in adolescent males prospectively predicted increased levels of internalizing symptoms (depression and anxiety) in late adolescence. It was postulated that reactive aggression would be robustly related to later internalizing problems, but only among adolescent males who had problematic family or peer social relationships. Participants were a racially diverse group of 289 adolescent males (Mean age = 16). Measures of reactive and proactive aggression, peer rejection, and poor parent–adolescent communication were examined as predictors of both depression and anxiety symptoms assessed approximately 3 years later. The interactive effects between the two facets of aggression and measures of peer rejection and poor parent–adolescent communication in predicting internalizing problems was also examined. Adolescents with high levels of reactive aggression were more likely to exhibit elevated internalizing problems during late adolescence, even when controlling for pre‐existing levels of anxiety/depression. However, this association only emerged for adolescents who had high levels of peer rejection and/or poor communication with their parent. Consistent with expectations, proactive aggression was unrelated to internalizing symptoms regardless of social relationship quality. Adolescent reactive, but not proactive, aggression is a risk factor for the development of internalizing problems. However, the findings suggest that interventions designed to foster positive social relationships among reactively aggressive youth may help protect them from developing significant internalizing problems over time. Aggr. Behav. 9999:1–10, 2013. © 2013 Wiley Periodicals, Inc.