The prevalence of marijuana use and perceptions of the prevalence of marijuana use was assessed in a sample of intercollegiate athletes and a separate sample of primarily first-year non-athlete students at a northwestern public university. Marijuana use prevalence in the non-athlete sample was higher than the prevalence found in nationwide surveys of drug use on college campuses. Current use of marijuana was greater in non-athletes than athletes, however, lifetime use was equivalent. The perceptions of prevalence of marijuana use among both athletes and non-athletes exceeded self-reported use in these groups. Students who used marijuana held higher perceptions of the prevalence of marijuana use among their campus peers and those believing that marijuana use was normative on campus were more likely to be current marijuana users themselves. The findings from this study have important implications for designing college drug prevention programs.