Overweight and obese children and adolescents often experience social adjusment difficulties, including higher rates of peer victimization and loneliness. Our primary goal was to examine the moderating influences of various aspects of organized activity involvement (i.e., intensity, duration, amount of physical activity, perceived importance, liking, and quality of adult- and peer relationships) on body mass index (BMI) and social adjustment relations. Results suggested that activity involvement moderated BMI-adjustment relations in certain instances. Specifically, fewer hours and less physical activity was associated with less loneliness among heavier adolescents. This study affirms the need for further research to address the impact that organized activity participation has on social adjustment among a variety of youth.