Urban populations disproportionately experience poor sexual outcomes, including high rates of teenage pregnancy and sexually transmitted infections. However, the contribution of substance use across adolescence to poor sexual outcomes in young adulthood has not been investigated in depth, despite offering opportunities for more targeted prevention. This study aimed to estimate joint trajectories of adolescent alcohol and marijuana use to determine if they relate differently to four sexual outcomes: multiple sexual partners, sex without a condom, teenage pregnancy, and contraction of a sexually transmitted infection in young adulthood (by age 25). Data came from a longitudinal study of urban youth followed from age 6 to age 25, with annual assessments during adolescence and young adulthood (n = 608). The sample showed high levels of sexual risk, with young adults on average having sex without a condom once in the past month, 28.5% having multiple sexual partners in the past month, one quarter having contracted a sexually transmitted infection, and over 60% of the women being pregnant as a teenager and 36% of the men having gotten a partner pregnant. Applying longitudinal latent profile analysis to estimate joint trajectories of alcohol and marijuana use from grades 8-12, we identified four classes representing high dual use, moderate alcohol use, moderate alcohol use with increasing marijuana use, and non-use. Class membership differently predicted all four outcomes investigated with high dual users having the highest level of teenage pregnancy and the increasing marijuana trajectory having the highest risk of engaging with multiple sexual partners in the past month. Results suggest implications for both sexual risk and substance use prevention for urban youth.