African Americans are disproportionately affected by HIV/AIDS and other sexually transmitted infections (STIs) relative to other racial/ethnic groups. Substance involvement has been linked to risky sexual behavior, an important risk factor for HIV/STI transmission, relatively early in the life course; yet such associations have not been found consistently among African Americans. Understanding of how substance involvement relates to risky sexual behavior among men and women over time and into midlife remains limited. The goal of this study was to examine the associations and pathways between substance involvement and risky sexual behavior over the life course in a community-based urban African American cohort (n=1242) followed prospectively from age 6 to 42 years. Using a combination of structural equation modeling and mediation testing, the study examined (1) prospective associations (from adolescence through adulthood) and within-life stage associations (in adolescence, young adulthood, and midlife) between substance involvement and risky sexual behavior, (2) the role of young adult social bonds as potential pathways linking substance use and risky sexual behavior over time, and (3) gender differences in the associations and pathways. The results revealed statistically significant positive associations between earlier substance involvement and subsequent risky sexual behavior over the life course among men and women. Greater adolescent substance use predicted greater midlife risky sexual behavior, partly through greater young adult substance problems and risky sexual behavior for both genders. Substance involvement was also positively correlated with sexual/risky sexual behavior in adolescence, young adulthood, and midlife among men and women. Although greater adolescent substance use predicted fewer young adult social bonds for both men and women, the latter was associated with decreased involvement in midlife risky sexual behavior among women only. Considered individually, young adult social bonds were not significant mediators of the adolescent substance use–midlife risky sexual behavior association for either gender. Given the complex pattern of associations and pathways between substance involvement and risky sexual behavior over time, public health interventions to address substance involvement among urban African Americans at any life stage, starting with adolescence, may have immediate and long-term effects, and direct and indirect effects on decreasing sex-related HIV/STI risk.