Regular physical activity is important for health benefits among youth, but disparities exist. This paper describes disparities in physical activity participation and sedentary behaviors among youth in the United States, provides intervention implications, and offers recommendations for future research focused on reducing disparities related to levels of physical activity. Secondary analysis of national accelerometer data showed that achievement of recommended levels of physical activity ranged across subgroups from 2% to 61%. Mean hours per day spent in sedentary behavior ranged from 5.5 to 8.5. The largest disparities were by gender and age. An improved understanding of correlates may inform the design of interventions to increase physical activity in targeted subgroups. Additional theoretically based research is needed to elucidate which factors contributing to physical activity disparities are amenable to change via intervention. To eliminate health disparities, changes in policies that have an impact on physical activity may be necessary to promote physical activity among high-risk youth.