Context: Evidence about long-term effects of preventive health services for youth with complex needs is lacking. Prime Time, a youth development intervention, aims to reduce pregnancy risk among vulnerable adolescent females seeking clinic services. Methods: In a randomized trial, 253 sexually active females aged 13-17 who were at high risk for pregnancy were assigned to the Prime Time intervention or usual clinic services. The 18-month intervention, initiated in 2007-2008, comprised regular meetings with case managers and participation in youth leadership groups. Trial participants completed surveys at baseline and 30 months. Regression analyses were used to evaluate differences between groups in sexual and psychosocial outcomes at follow-up. Results: At 30 months, the intervention group reported more months of consistent condom use (adjusted means, 1.8 vs. 1.1) and dual contraceptive use (0.9 vs. 0.3) in the past seven months than did controls. The intervention was most effective in promoting consistent use among participants with relatively high levels of connectedness to family or school. Fifteen percent of intervention participants, but only 6% of controls, reported having abstained from sex in the past six months (adjusted odds ratio, 2.9). Moreover, among high school graduates, those in the intervention group were more likely than those in the control group to have enrolled in college or technical school (72% vs. 37%; odds ratio, 4.5). Conclusion: Health services grounded in a youth development framework can lead to reductions in sexual risk among vulnerable youth that are evident one year following conclusion of services.