Rape awareness and prevention programs are common on college campuses and a potentially useful way to reach large numbers of young adults. One largely unexamined potential mediator or moderator of program effectiveness is the personal knowledge of student audiences. In this study, we assess the prevalence of knowing a victim and, notably, a perpetrator of sexual assault. A stratified random sample of 2,400 undergraduates was recruited for an online survey about sexual assault. A total of 53.5% participated and yielded a sample representative of the student body. Sixteen questions were modified from the Sexual Experiences Survey to assess whether participants knew a victim of any one of eight types of sexual assault. Findings indicate that students begin college with considerable personal knowledge of sexual assault victimization and perpetration. Nearly two thirds (64.5%) reported that they know one or more women who were a victim of any one of eight types of sexual assault, and over half (52.4%) reported that they know one or more men who perpetrated any of the types of sexual assault. Most students reported knowing victims and perpetrators of multiple types of assault. Knowledge varied substantially by gender and ethnicity. Students’ preexisting personal knowledge should be included in assessments of program effectiveness and, ideally, in program design.