Positive youth development is thought to be essential to the prevention of adolescent risk behavior and the promotion of thriving. This meta-analysis examined the effects of positive youth development interventions in promoting positive outcomes and reducing risk behavior. Ten databases and grey literature were scanned using a predefined search strategy. We included studies that focused on young people aged 10-19 years, implemented a positive youth development intervention, were outside school hours, and utilized a randomized controlled design. Twenty-four studies, involving 23,258 participants, met the inclusion criteria and were included in the analysis. The impact of the interventions on outcomes including behavioral problems, sexual risk behavior, academic achievement, prosocial behavior and psychological adjustment were assessed. Positive youth development interventions had a small but significant effect on academic achievement and psychological adjustment. No significant effects were found for sexual risk behaviors, problem behavior or positive social behaviors. Intervention effects were independent of program characteristics and participant age. Low-risk young people derived more benefit from positive youth development interventions than high-risk youth. The studies examined had several methodological flaws, which weakened the ability to draw conclusions. Substantial progress has been made in the theoretical understanding of youth development in the past two decades. This progress needs to be matched in the intervention literature, through the use of high-quality evaluation research of positive youth development programs.