Most studies on sexual behavior outcomes are restricted to adolescents. However, rates of sexually transmitted diseases (STDs) are highest among young adults. This study examined social–ecological predictors in adolescence that predict risky sexual behavior in young adulthood. Using longitudinal data, logistic regression was used to determine social–ecological factors that predict early sexual debut and a high number of lifetime sexual partners among 3,109 young adults. Risk-taking was associated with early sexual debut and a high number of lifetime sexual partners. Father–child connectedness decreased the odds of early sexual debut and a high number of lifetime sexual. School connectedness also decreased the odds of early sexual debut and a high number of lifetime sexual. There was no relationship between mother–child connectedness and the risky sexual behavior. The influence of childhood factors may encompass young adulthood. Personality traits could be used by programs aimed at preventing STD–related behaviors to characterize those at higher risk for risky sexual behavior. These programs also could be more effective by developing approaches that foster parent–child connectedness, and by gaining a greater understanding of the mechanisms through which school connectedness protects against risky sexual behavior, which could decrease the prevalence of risky sexual behaviors, and subsequently lower the rates of STDs among young adults.