Young men are more likely than young women to engage in behaviors that threaten their health, including alcohol and drug use, risky driving, and becoming injured by others. The explanation of these sex differences is the focus of this paper. Findings from nationwide samples of high school seniors are consistent with a model that posits personal characteristics related to commitment to educational and religious institutions and to the roles of the sexes in this society; opportunity factors; and drug use patterns as explanatory factors of the sex differences. Controlling in multivariate analyses for these factors reduces or eliminates the bivariate sex differences in the health-threatening behaviors. The number of cigarettes smoked during the last month shows no bivariate sex differences; however, when the controls are introduced, there emerges a clear sex difference to the disadvantage of young women. (Author)