Since the 1980s, the age at which U.S. teenagers, especially minority youth, begin having sex has decreased. There is limited information on the relationship between early sexual initiation and subsequent risky sexual behaviors. A sample of 1,287 urban minority adolescents completed three surveys in seventh and eighth grade, and 970 completed a follow-up in 10th grade. Logistic regression was used to test the effects of timing of initiation on 10th-grade sexual behaviors and risks, adjusting for gender, ethnicity and age. At baseline, 31% of males and 8% of females reported sexual initiation; by the 10th grade, these figures were 66% and 52%, respectively. Recent intercourse among males increased from 20% at baseline to 39% in eighth grade; 54% reported recent sex and 6% had made a partner pregnant by 10th grade. Among females, recent intercourse tripled from baseline to eighth grade (5% to 15%); 42% reported recent sex and 12% had been pregnant by grade 10. Early initiators had an increased likelihood of having had multiple sex partners, been involved in a pregnancy, forced a partner to have sex, had frequent intercourse and had sex while drunk or high. There were significant gender differences for all outcomes except frequency of intercourse and being drunk or high during sex. Minority adolescents who initiate sexual activity early engage in behaviors that place them at high risk for negative health outcomes. It is important to involve parents and schools in prevention efforts that address sexual initiation in early adolescence and that target youth who continue to place themselves and their partners at risk.