The effects of a primary prevention social norm intervention on binge drinking among 1st-year residential college students were examined. Six hundred thirty-four students attending a medium-sized public university in the South were randomly assigned to receive a two-phase social norm intervention or the standard campus psychoeducational prevention program. At posttest, no differences were found between intervention and control group students on any of the alcohol use and alcohol-use risk factor measures. Significant subgroup differences were found by stage of initiating binge drinking behaviors, for frequency of alcohol use, F(3, 507) = 3.69, p = .01; quantity of alcohol use, F(3, 507) = 2.51, p = .05; and social norms, F(3, 505) = 2.53, p = .05. These findings suggest the need for tailoring social norm binge drinking interventions to students' stage of initiating heavy drinking and carefully monitoring for potential negative, as well as positive, effects of norm-based prevention messages.