OBJECTIVE: To analyze sources of racial and gender disparities in adolescent obesity prevalence in the United States using Oaxaca-Blinder decomposition. METHODS: Data were obtained from the National Youth Physical Activity and Nutrition Study, a 2010 nationally representative study of 9th-12th grade students. Obesity status was determined from objective height and weight data; weight-related behaviors and school, home, and environmental data were collected via questionnaire. Oaxaca-Blinder decomposition was used to independently analyze racial and gender obesity prevalence differences (PD), i.e., comparing Black girls to White girls, and Black girls to Black boys. RESULTS: Overall, measured characteristics accounted for 46.8% of the racial PD but only 11.9% of the gender PD. Racial PD was associated with Black girls having less fruit/vegetable access at home, obtaining lunch at school more often, and playing fewer sports than White girls. Gender PD was associated with differential associations between physical activity (PA) measures-including total activities in the past year and days of moderate to vigorous physical activity (MVPA) in the past week-and obesity. CONCLUSIONS: School lunch and home food environmental variables accounted for racial disparities, but not gender disparities, in obesity prevalence. Gender differences in mechanisms between PA and obesity should be explored further.