Importance: Preventing early pregnancy among vulnerable adolescents requires innovative and sustained approaches. Prime Time, a youth development intervention, aims to reduce pregnancy risk among adolescent girls seeking clinic services who are at high risk for pregnancy. Objective: To evaluate sexual risk behaviors and related outcomes with a 24-month postbaseline survey, 6 months after the conclusion of the Prime Time intervention. Design: Randomized controlled trial. Setting: Community and school-based primary care clinics. Participants: Of 253 sexually active 13- to 17-yearold girls meeting specified risk criteria, 236 (93.3%) completed the 24-month follow-up survey. Intervention: Offered during an 18-month period, Prime Time includes case management and youth leadership programs. Main Outcome Measures: Self-reported consistency of condom, hormonal, and dual-method contraceptive use with most recent male sex partner and number of male sex partners in the past 6 months. Results: At 24-month follow-up, the intervention group reported significantly more consistent use of condoms, hormonal contraception, and dual-method contraception than the control group. Intervention participants also reported improvements in family connectedness and self-efficacy to refuse unwanted sex, and reductions in the perceived importance of having sex.Nobetween-group differences were found in the number of recent male sex partners. Conclusions and Relevance: This study contributes to what has been a dearth of evidence regarding youth development interventions offered through clinic settings, where access to high-risk adolescents is plentiful but few efforts have emphasized a dual approach of strengthening sexual and nonsexual protective factors while addressing risk. Findings suggest that health services grounded in a youth development framework can lead to long-term reductions in sexual risk among vulnerable youth.