This paper examines the relationship that social fraternity and sorority membership has with binge drinking incidence and frequency among 18-24 year old full-time 4-year college students who participated in the 1995 National College Health Risk Behavior Survey. To net out unobserved heterogeneity, several measures of situational and total alcohol use are entered into the regressions as explanatory variables. Fraternity membership coefficients are substantially reduced in size, but remain large and highly significant, suggesting a causal effect on binge drinking. Otherwise, the estimates identify idiosyncratic selection into fraternities and binge drinking across students with similar overall drinking profiles. Particularly notable is that behavior by underage students appears to drive the relationship.