The primary purposes of this study were to compare (a) physical activity participation, screen-time habits, obesity, and (b) reported reasons for lack of participation in sport, between a nationally representative sample of Irish children with and without autism spectrum disorder (ASD). Participation in moderate to vigorous activity, light activity, and sports was significantly lower among the group with ASD. On examination of screen time variables, no significant differences were seen between groups. However, time spent watching TV was higher among children with ASD. Overweight or obese status was more prevalent among the group with ASD (34.4 vs. 24.7%). The findings are discussed in relation to international statistics on youth physical activity, screen-time, and weight status, and recommendations are provided for future research.