This study presents the results of an efficacy evaluation of a web-based brief motivational alcohol prevention/intervention program called "Michigan Prevention and Alcohol Safety for Students" (M-PASS). Four on-line sessions providing individually-tailored feedback were delivered to first-year college students over 9 weeks. Non- and low-risk drinking participants received risk prevention, while high-risk drinking participants received a risk-reduction intervention. Both intervention and control groups were surveyed at baseline and at a 3-month follow-up. Analysis showed positive effects for both men and women on stage of change, drinking behavior, drinking motivation and attitudes, and use of risk-reduction strategies. These results provided evidence of efficacy and found that M-PASS had both intervention and prevention effects, making it unique among currently developed brief alcohol interventions for college students. (Contains 1 figure and 2 tables.)