Objective: This study examined the associations between college students' self-reported alcohol use and corresponding collateral reports and identified factors that influence agreement between both sets of reports. Participants/Methods: Subject-collateral pairs (N = 300) were recruited from undergraduate psychology courses. Results: Data yielded moderate correlations between subject-collateral pairs for all alcohol use measures, whereas discrepancy analyses revealed a tendency for subjects to report greater alcohol use relative to collateral reports. Greater subject-collateral agreement regarding frequency of subject alcohol use was predicted by a greater frequency of shared drinking occasions between the dyads, lower subject self-reported drug use, and lower levels of collateral guessing, whereas greater correspondence for quantity of alcohol consumed was predicted by fewer subject self-reported alcohol-related negative consequences, lower levels of subject self-reported drug use, and lower levels of alcohol ingestion among collaterals. Conclusions: College students appear to provide reasonably accurate self-reports of their alcohol use. (Contains 3 tables.)