Body mass index classification, physical activity (PA), and sedentary behaviors were compared in adolescents with autism spectrum disorder (ASD) to typically developing adolescents. Participants included 42,747 adolescents (ASD, n = 915) from the 2011-2012 National Survey of Children's Health. After controlling for covariates, adolescents were more likely to be overweight and obese, and less likely to engage in regular PA versus typically developing adolescents (p's < 0.05). Increased odds for overweight and obesity were attenuated after adjustment for PA. Higher autism severity was associated with increased odds of overweight and obesity and decreased odds of PA, sport, and club participation. These findings suggest adolescents with ASD are in need of targeted programs to decrease obesity and increase physical activity.