Men and women living in randomly selected 1st-year dormitories participated in tailored single-sex sexual assault prevention or risk-reduction programs, respectively. An evaluation of the men’s program is presented (N = 635). The program incorporated social norms and bystander intervention education and had an impact on self-reported sexual aggression and an effect on men’s perceptions that their peers would intervene when they encountered inappropriate behavior in others. Relative to the control group, participants also reported less reinforcement for engaging in sexually aggressive behavior, reported fewer associations with sexually aggressive peers, and indicated less exposure to sexually explicit media.