Research has found the early onset of sexual activity (having sexual intercourse before age 13) among adolescents to be related to teen pregnancy and a range of health-risk behaviors and higher rates of sexually transmitted infections (STIs) and HIV/AIDS. These findings are most prevalent in urban African American adolescents. Using a sample of 299 sexually active African American adolescents living in public housing developments in a large Northeast and a large Mid-Atlantic city, this study assesses the influence of family, peers, and the individual on the age of onset of sexual intercourse. All participants completed surveys in their housing developments. Results indicate an average age of onset of 14. Males reported a significantly younger age of onset and more sexual partners than females. Exposure to delinquent peers and self-efficacy were significant predictors of age of onset. Implications for practice are discussed.