Based on sexual selection theory, we hypothesized that sex differences in mating effort and social competitiveness-and subsequent sex differences in sexual and competitive motivations for participating in drinking games-are responsible for the well-documented sex differences in college students' drinking game behaviors. Participants in a cross-sectional study were 351 women and 336 men aged 17 to 26. In a mediation model, we tested sex differences in mating effort, social competitiveness, sexual and competitive motivations for participating in drinking games, drinking game behaviors, and alcohol-related problems. Men participated in drinking games more frequently, consumed more alcohol while participating in drinking games, and experienced more problems associated with drinking. These sex differences appeared to be partially mediated by mating effort, social competitiveness, and sexual and competitive motivations for participating in drinking games. Drinking games are a major venue in which college students engage in heavy episodic drinking, which is a risk factor for college students' behavioral and health problems. Thus, the functional perspective we used to analyze them here may help to inform public health and university interventions and enable better identification of at-risk students.