This study considers the long-term mental health implications of organized youth sport participation, informed by an accumulation model of health, the Sport Commitment Model, and a life course perspective. Using data from the National Sports and Society Survey (N = 3,931) and multiple regression analyses, results indicate that adults who continually played organized youth sport had fewer depressive and anxiety symptoms compared with those who played and dropped out and those who never played. Dropouts had worse mental health than those who never played. Furthermore, among dropouts, reported interpersonal reasons for dropping out of organized sport were consistently associated with subsequent mental health but some structural factors also mattered. These findings point to a need to improve the interpersonal and structural environments of organized youth sport.