OBJECTIVE: Retrospective summary, followback (retrospective diaries), and prospective daily diary measures of alcohol use among college students were compared across 29 days. METHOD: Participants were college students (n = 176; 60.2% female). Similarities in the three web-based reporting methods and both between-persons (i.e., gender, past drinking behavior, fraternity/sorority affiliation, average drinking behavior during the study period) and within-person (i.e., daily number of drinks, weekend days, Halloween, and week of study) predictors of concordance between reports of followback and prospective diaries were analyzed. RESULTS: On prospective diaries, students reported a greater number of maximum drinks (compared with followback only) and a greater number of heavy drinking days in the past 2 weeks (compared with both followback and retrospective summary measures). In followback compared with prospective diaries, students tended to provide inflated accounts of their drinking behavior when reporting about occasions with greater typical drinking (i.e., weekends, Halloween) and deflated accounts of their drinking on their own heavier drinking days, especially if they were affiliated with a fraternity/sorority. Women and students who drank more on average across study days tended to provide deflated estimates of their day-to-day drinking in followback compared with prospective diary. CONCLUSIONS: Understanding the concordance and discordance in self-reported alcohol use is an important area for continued research efforts.