Objective: To determine whether completing a pre-enrollment Web-based alcohol brief motivational intervention (BMI) increased student retention and reduced student alcohol-related violations. Participants: Fall 2011 (3,364) and Fall 2012 (3,111) entering cohorts of all first-year students at a midwestern state university. Method: Students completing the brief intervention (BI) were compared to students not completing the BI. Retention was tracked for four years for the 2011 cohort and three years for the 2012 cohort. Campus and community alcohol violations were tracked for two academic years following enrollment. Kaplan-Meier survival analysis and Cox regression were used to test retention survival. Logistic regression was used to test campus and community violations. Results: Students in both cohorts who completed the BI had significantly higher retention and significantly fewer alcohol-related violations than noncompleters. Conclusions: Population-level Web-based BIs help prevent student dropout and decrease alcohol-related violations, with impacts extending multiple years. Web-based BI is an efficacious population-level prevention tool.