Overweight children and adolescents often experience negative psychological consequences. Organized activity involvement may be one experience that protects against such negative adjustment. The primary goal of this study was to gain a more comprehensive understanding of the relation between body mass (BMI), organized activity involvement, and adjustment (i.e., self-worth, depressive symptoms, peer victimization, loneliness). This study examined BMI as it relates to adjustment in 150 adolescents at an urban high school. The study also examined the moderating influence of activity involvement (i.e., intensity, duration, physical activity, importance, liking, quality of adult- and peer relationships) upon the BMI-adjustment links. Results indicated that BMI was not linked with negative psychosocial adjustment. Activities that were rated as being particularly important and included quality relationships with adults and peers were associated with less loneliness. A significant BMI X gender interaction effect suggested that as BMI increased for females, peer victimization decreased. Activities also moderated the BMI-adjustment relations. For example, at higher number of overall hours per week and amount of physical activity, heavier adolescents reported more loneliness, while at lower levels of overall hours per week and physical activity, heavier adolescents reported less loneliness. This study affirms the need for further research to address the impact that organized activity participation has upon adjustment.