Objective: Reduce college student at-risk drinking (ARD) using a Web-based brief motivational alcohol prevention/intervention called "Michigan Prevention and Alcohol Safety for Students" (M-PASS). Participants: Participants included 1,137 randomly sampled first-year college students, including 59% female, 80% white, and averaged age 18.1 years. Methods: Intervention group participants (n = 616) attended 4 online M-PASS sessions, receiving feedback tailored to individual drinking patterns and concepts from 4 behavior change theories. Control group participants (n = 521) completed a mid-phase survey, and both groups were surveyed at baseline and posttest. Results: Evidence of M-PASS's efficacy was found. The intervention was associated with advanced stage of change, lower tolerance of drinking and drink/driving, fewer reasons to drink, and use of more strategies to avoid ARD. Preliminary evidence of behavioral change was also found. Efficacy was greater for women than men. Conclusions: Web-based programs may be useful in reducing alcohol-related risk among college students. Further evaluation is needed. (Contains 2 tables.)