Objective: This prospective study examined attitudes (ie, hostility toward women, acceptance of rape myths), peer influences (ie, peer pressure to have sex, peer approval of forced sex), and risky behaviors (ie, high-risk alcohol use, number of sexual partners) as possible mediators of the association between fraternity membership and sexual aggression. Participants: The sample included 424 males recruited as freshmen from a large state university in the southeastern United States. Methods: Respondents completed survey measures in their first, second, and third years of enrollment at the university. Results: Path analyses revealed that the prospective effect of fraternity membership on sexual aggression was mediated by high-risk alcohol use. Conclusions: The findings indicate that high-risk alcohol use accounts for much of the association between fraternity membership and sexual aggression. (Contains 1 figure and 2 tables.)