The study found that participation in an organized sport during adolescence was linked with higher levels of physical activity and better subjective health during young adulthood after controlling for participation in general physical activities (e.g., jogging, biking, and skateboarding) during adolescence. Participation in sports as an adolescent was associated with more positive self-beliefs 1 year later; in turn, positive self-beliefs were linked with higher levels of moderate to vigorous physical activity and better subjective health 6 years later. Thus, positive self-beliefs partially mediate the link between adolescents' participation in sports and moderate to vigorous physical activity and subjective health in young adulthood. This study involved a subsample of 8,152 high-school students who participated in the National Longitudinal Study of Adolescent Health. All of the participants had completed data for the sampling weights at all three waves of data collection. Add Health assessed physical activity with self-reported items used and validated in other large-scale studies. Subjective health was assessed at wave III with the question, "In general, how is your health?" Five response options ranged from "poor" to "excellent." A dichotomous variable that represented participation in sports during adolescence was created from the wave I in-school questionnaire. A list of sports was provided from which respondents selected the ones in which they participated. Positive self-beliefs were measured by taking the mean of 11 items that assessed positive beliefs about the self obtained from wave II of Add Health. 5 tables, 2 figures, and 42 references