Concern exists that youth who spend a lot of time participating in organized out-of-school activities (e.g., sports) are at-risk for poor developmental outcomes. This concern - called the over-scheduling hypothesis - has primarily been assessed in terms of adolescent adjustment. This longitudinal study of a nationally representative sample of 1,115 youth (ages 12-18) assessed long-term relations between intensity of participation during adolescence and adjustment at young adulthood (ages 18-24). Time diaries measured intensity as hours per week of participation. Results showed that, controlling for demographic factors and baseline adjustment, intensity was a significant predictor of positive outcomes (e.g., psychological flourishing, civic engagement, educational attainment) and unrelated to indicators of problematic adjustment (e.g., psychological distress, substance use, antisocial behavior) at young adulthood.