Individuals with Autism Spectrum Disorders (ASDs) are at increased risk for poor psychosocial outcomes as adults. We described community and social participation in adolescents with ASDs as they transitioned from adolescence to adulthood, and identified adolescent factors associated with community and social participation outcomes in adulthood. We performed a secondary data analysis of a nationally representative cohort using the National Longitudinal Transition Study 2 and observed a significant decrease in community participation from adolescence to adulthood (63 to 46 %); social participation remained stable. The presence of case management in adolescence was associated with increased community and social participation in adulthood. Case management may be crucial for optimal levels of participation among adults with ASDs.