African American male youth disproportionately report involvement with multiple sexual partners, which increases their risk for sexually transmitted infections and initiation of unplanned pregnancies. Little is known about the developmental precursors of sexual partner trajectories among African American male youth. Moreover, few studies focus on the many African American youth who evince highly conventional sexual partner trajectories, i.e., youth who have only one partner or abstain from sexual activity across time. Using four waves of data from a longitudinal study, we hypothesized that an accumulation of social and economic disadvantages in early adolescence would negatively influence youths' conventional sexual partner trajectories in late adolescence. We expected these disadvantages to affect youths' receipt of protective family processes and their reports of a set of intrapersonal processes (self-regulation, hope, and low levels of anger) linked to generally conventional behavior. Hypotheses were tested with data from 315 African American male youth from 11 to 18.5 years of age and their primary caregivers. Our results supported the hypotheses. Socioeconomic disadvantages during preadolescence predicted less involvement in conventional sexual partner trajectories from ages 16 to 18.5 years. This association was mediated by protective family processes and a set of interrelated intrapersonal protective processes. Preventive interventions designed to promote protective parenting and intrapersonal processes can be expected to promote sexual behavior trajectories characterized by abstinence or relations with very few partners.