Importance of peer counselor post-training supervision on Motivational Interviewing microskills and post-intervention drinking outcomes were evaluated in a sample of heavy drinking undergraduate students completing BASICS (Dimeff et al., 1999). Two peer counselor groups were trained using identical protocols. Post-training, one group was randomized to receive supervision, while the other received no supervision. Groups were subsequently compared on MI microskills. College students (N=122) were randomly assigned to either assessment-only control, supervision, or no supervision groups and completed a BASICS intervention. Post-intervention drinking outcomes were examined. Results suggested supervision aided peer counselors in reducing use of closed-ended questions. Both treatment groups reduced total drinks per week and heavy drinking behaviors compared to control. No differences on peak BAC or alcohol related consequences were observed. Differences in supervision did not influence drinking outcomes; however post-training supervision for peer counselors deficient in MI microskills may be needed to improve BASICS fidelity.