This study evaluated the efficacy of two brief personalized normative feedback interventions aimed at reducing heavy drinking among mandated college students (N = 135). Students were randomly assigned to one of two conditions: Web-based assessment with self-guided personalized normative feedback (SWF) or Web-based assessment with counselor-guided personalized normative feedback (CWF). Results indicated that students in the CWF condition reported significantly greater reductions in weekly drinking quantity and binge drinking frequency than those in the SWF group at follow-up (M = 8 months). Students in the CWF group also reported significantly greater reductions in estimates of peer drinking from baseline to the follow-up assessment than students in the SWF group. In addition, changes in estimates of peer drinking partially mediated the effect of the intervention on changes in drinking. Results suggest that counselor-guided feedback may be more effective in reducing drinking among mandated students relative to self-guided feedback in the long term.