Health-compromising lifestyles involve stable patterns of behavior and are associated with high-risk social environments and accelerated developmental trajectories. Developmentally, antisocial behavior is associated with such lifestyles. Mediational models predicting a measure of lifetime average sexual risk behavior assessed over a 10-year period (from ages 13-14 to 22-23 years) were examined for a sample of at-risk young men. The measure included years of abstinence from intercourse as well as levels of 3 key heterosexual indicators of risk: frequency of intercourse, number of intercourse partners, and condom use. Predictors included lifetime average measures of contextual, family, and peer process variables and individual behaviors. In addition, similar models for prediction of STD contraction were assessed. A younger age of onset of intercourse was associated with higher numbers of intercourse partners after onset. As hypothesized, findings indicated mediational associations of socioeconomic status, parental monitoring, deviant-peer association, antisocial behavior, and substance use in the prediction of sexual risk behavior. Lower condom use also predicted STD contraction.