The prevention of obesity in children with DD is a pressing public health issue, with implications for health status, independent living, and quality of life. Substantial evidence suggests that children with developmental disabilities (DD), including those with intellectual disabilities (ID) and autism spectrum disorder (ASD), have a prevalence of obesity at least as high if not higher than their typically developing peers. The paper reviews what is known about the classic and unique risk factors for childhood obesity in these groups of children, including dietary, physical activity, sedentary behavior, and family factors, as well as medication use. We use evidence from the literature to make the case that primary prevention at the individual/family, school and community levels will require tailoring of strategies and adapting existing intervention approaches.