Physical activity promotion is of need for youth with developmental disabilities. Parental perceptions of physical activity benefits may influence youth behaviors. This study investigated the relationship between parental beliefs on the importance of physical activity and physical activity levels among youth with disabilities. Parents and caregivers of 113 youth with disabilities reported on the perceived benefits of physical activity, the child's physical activity level, and demographic information. Linear regression analyses to examine the relative association between parental perceived benefits and child physical activity (R[superscript 2] = 0.19) indicated that physical activity level was predicted by parental beliefs and child gender. Health promotion for youth with disabilities should consider educating parents and caregivers of physical activity benefits, in addition to creating more opportunities.