Objective: Although a variety of sexual assault prevention programs are currently available to college health professionals, there is a dearth of information about the effect of these programs on sexual assault victimization rates. Participants: The authors evaluated the efficacy of a sexual assault prevention program for first-year students at a college in the Northeast (N = 1,982). Methods: They used a retrospective cohort design and assessed the prevalence of sexual assault victimization among students exposed to the sexual assault prevention program and students 1 year their senior who were not exposed. Results: Students who had no exposure were more likely to report that they were sexually assaulted during their first year of college (odds ratio = 1.74, 95% confidence interval [1.32-2.29]). Results suggest that the program was effective for males and females, but not for students with a prior history of sexual assault victimization. Gay, lesbian, and bisexual students were at increased risk for victimization as compared with heterosexual students, and students who drank alcohol or engaged in binge drinking were at increased risk as compared with alcohol abstinent students. Conclusions: Findings suggest that this program had a positive effect on victimization rates for certain sub-groups of students. (Contains 1 figure and 3 tables.)