Objective: Analyze evidence of the benefits of physical activity for youth with developmental disabilities. Data sources: Key word searches for "disability," "physical activity," "exercise," "fitness," and "sport" in major databases. A total of 3263 citations was found. STUDY INCLUSION/EXCLUSION CRITERIA: Systematic reviews and articles about studies quantitatively examining the effects of physical activity in youth with developmental disabilities ages 0 to 20 years were included. Only articles published in English in peer-reviewed journals were included. Data extraction: A Measurement Tool to Assess Reviews criteria were used for systematic reviews; Grading of Recommendations, Assessment, Development, Evaluation criteria were used for observational studies; and Population, Intervention, Comparison, Outcome criteria were used for all studies. Data synthesis: Data, shown in table format, were synthesized in relation to five research questions. Results: Three systematic reviews and 14 studies were reviewed. Strong evidence indicated that children and adolescents with developmental disabilities derive health benefits from participation in group exercise programs, treadmill training, or therapeutic riding/hippotherapy. Lesser levels of evidence indicated that health benefits might be present for adapted skiing or aquatic programs. Documented benefits of physical activity include improvements in aerobic capacity, improved gross motor function, and high levels of participant/parent satisfaction. Conclusions: Evidence exists that physical activity is beneficial for youth with developmental disabilities. Further research studies are needed that are of greater scientific rigor including larger sample sizes, control groups, and stringent, replicable methodology.