The purpose of this study was to explore the association between participation in organized sport and a broad array of mental health difficulties among US children and adolescents. The data (cross-sectional) were from Data Release 3.0 (one-year follow-up visits on the full cohort) of the Adolescent Brain Cognitive Development (ABCD) study-a broadly representative sample of 11,235 US children and adolescents aged 9 to 13 years. Parents/guardians provided self-reports of their child's mental health difficulties using the Child Behavior Checklist. To assess participation in organized sport, children and adolescents were categorized into one of four groups: 1) participation in team sport, 2) participation in individual sport, 3) participation in team and individual sport, and 4) non-sport participation. Participation in team sport compared to non-sport participation was associated with 10% lower anxious/depressed scores, 19% lower withdrawn/depressed scores, 17% lower social problems scores, 17% lower thought problems scores, and 12% lower attention problems scores. Participation in team sport compared to non-sport participation was also associated with 20% lower rule-breaking behavior scores for females (compared to males). Conversely, participation in individual sport compared to non-sport participation was associated with 16% higher anxious/depressed scores, 14% higher withdrawn/depressed scores, 12% higher social problems scores, and 14% higher attention problems scores. Participation in both team and individual sport compared to non-sport participation was associated with 17% lower rule-breaking behavior scores for females (compared to males). Results indicate that team sport participation was associated with fewer mental health difficulties, whereas individual sport participation was associated with greater mental health difficulties. The findings complement previous research suggesting that team sport participation may be a vehicle to support child and adolescent mental health. Additional research is needed to determine to what extent, and under what circumstances, participation in individual sport may be problematic for younger cohorts.