Objective: Sexual and dating violence (SV/DV) on college campuses is a pervasive problem with far-reaching implications for public health. This paper describes the development and evaluation of a widely disseminated SV/DV primary prevention program, the Red Flag Campaign (RFC). Participants and Methods: An online survey was administered to 203 freshmen at a southeastern US university, of whom 82% reported exposure to the RFC in the previous month. Results: College students exposed to the RFC reported greater efficacy for intervening as a bystander compared to those students who were not exposed. These results held when looking at exposure to RFC "messages" specifically, but not RFC "events." Conclusions: This evaluation offers preliminary evidence that the RFC is effective at increasing determinants of prosocial bystander behavior, the enactment of which could reduce SV/DV on college campuses. Implications and recommendations for college personnel implementing the RFC are discussed.