Researchers in the social norms area have previously focused primarily on alcohol consumption, paying comparatively less attention to drug use and sexual behavior. The major purposes of this study were to (1) compare perceptions of peer norms in the areas of alcohol use, drug use, and sexual behavior with actual behavior and (2) determine if a relationship existed between a student's perceptions of normative behavior and a student's actual behavior. Participants were 833 college students at a large, public university in the Northeast. Study participants overestimated alcohol use, drug use, and sexual behavior among their peers. There was also a positive relationship between actual behavior and perceived peer norms, although the effect sizes for all behaviors were small to moderate. The authors provide further support for the tenets of social norms theory and suggest that social norms interventions are appropriate both campus-wide and to targeted high-risk groups. (Contains 3 tables.)