Objective: To understand how missing data may influence conclusions drawn from campus sexual assault surveys. Methods: We systematically reviewed 40 surveys from 2010-2016. We constructed a pseudo-population of the total population targeted across schools, creating records proportional to the respective response rate and reported sexual assault prevalence. We simulated the effects of 9 scenarios where the sexual assault prevalence among nonresponders differed from that of responders. Results: The surveys represented a total female undergraduate population of 317,387 with only 77,966 (24.6%) survey responses. Among responders, 20.4% reported experiences of sexual assault. However, prevalence of sexual assault could theoretically range from 5.0 to 80.4% under extreme assumptions about prevalence in nonresponders. Smaller, but still significant differences were observed with less extreme assumptions. Conclusions: Missing data are widespread in campus sexual assault surveys. Conclusions drawn from these incomplete data are highly sensitive to assumptions about the sexual assault prevalence among nonresponders.