This study aimed to examine how environmental factors are associated with physical activity (PA) and screen-time (ST) among children with and without ASD (n = 1380 and 1411, respectively). For TD children, the absence of a bedroom television and neighborhood support were associated with PA. For children with ASD, no environmental factors were associated with PA. Regarding ST, the presence of a bedroom television, absence of limits on ST, lack of neighborhood amenities and support, and adverse neighborhood factors were all associated with ST among TD children. For children with ASD, the presence of a bedroom television and the absence of limits on ST were associated with ST. Potential explanations for this dichotomy and suggestions for future research are discussed.