This study examines the relationship between binge drinking and sexual behavior in nationally representative data on age 18–24 four-year college students. For having sex, overall or without condoms, large and significant positive associations are eliminated upon holding constant proxies for time-invariant sexual activity and drinking preferences. However, strong relationships persist for sex with multiple recent partners, overall and without condoms, even controlling for substance use, risk aversion, mental health, sports participation, and sexual activity frequency. Promiscuity is unrelated with non-binge drinking but even more strongly related with binge drinking on multiple occasions. Results from a rudimentary instrumental variables strategy and accounting for whether sex is immediately preceded by alcohol use suggest that binge drinking directly leads to risky sex. Some binge drinking-induced promiscuity seems to occur among students, especially males, involved in long-term relationships. Effects are concentrated among non-Hispanic whites and are not apparent for students in two-year schools.