Purpose: Internalizing conditions, such as anxiety and depression, and difficulties with developing and maintaining friendships are common among autistic children and adolescents. Participation in extracurricular activities may buffer against these challenges as they provide naturalistic opportunities to bring peers with shared interests and skills together. As such, the purpose of the current study was to examine associations between sport and club participation and (1) friendship success and (2) co-occurring anxiety and depression in a large sample of autistic youth. Methods: Secondary analysis was performed using data from the 2018-2019 National Survey of Children's Health. Participants were 562 autistic children (ages 6-11 years) and 818 autistic adolescents (ages 12-17 years). Within each age group, a series of binary logistic regression analyses were conducted. Results: Club participation was not associated with friendship or internalizing conditions. However, participation in sports was positively associated with friendship success among both children (OR = 2.07, p = 0.006) and adolescents (OR = 2.35, p = 0.001). Results also found that adolescents who participated in sports were 34% less likely to have diagnosis of depression (p = 0.048). Conclusion: Findings suggest that participation in sports may play a meaningful role in protecting against depression during adolescence and serve as a context for friendship development across childhood and adolescence. Future research should address barriers to extracurricular activity participation and identify the specific components of sports that are most beneficial to autistic youth to inform activity offerings and the development of interventions targeting friendship formation and mental health outcomes.