To assess whether adolescent marijuana exposure represents a modifiable predictor of risk of sexually transmitted infections as adults, we used nationally representative, longitudinal data from Waves I (1994-1995, adolescence) and III (2001-2002, adulthood) of the National Longitudinal Study of Adolescent Health (N = 10,738) to examine racial and gender differences in associations between adolescent marijuana use, current use, and peer use and adulthood multiple partnerships, self-reported sexually transmitted infections, and biologically confirmed sexually transmitted infections. The risk of sexually transmitted infections as adults was predicted by adolescent marijuana use in all groups except Black women and by peer marijuana use among Black men. Adolescents who use or have friends who use marijuana constitute priority populations for sexually transmitted infection prevention.