Neighborhood disadvantage in early adolescence may help explain racial and ethnic disparities in obesity during the transition to adulthood; however the processes may work differently for males and females and for minority groups compared to Whites. The present study examines the relationship between neighborhood disadvantage and young adult obesity and the extent to which it contributes to racial/ethnic disparities among males and females. Data are from waves I and III of The National Longitudinal Study of Adolescent Health (Add Health), a nationally representative sample of adolescents administered between 1994 and 2002. The final sample of 5,759 adolescents was 54% female, 63% White, 21% African American, 16% Hispanic, and 14 years of age, on average, at wave I. Using hierarchical logit models and controlling for prior obesity status, findings indicate that, for females, adolescent neighborhood disadvantage partially explains racial/ethnic disparities in young adult obesity. Further, neighborhood disadvantage increases the odds of becoming obese for adolescent females in a curvilinear form, and this relationship significantly varies between Whites and Hispanics. Neighborhood disadvantage does not increase the risk of obesity for males, regardless of race/ethnicity. Implications for obesity prevention are discussed.