Background: The rise in adolescent obesity has become a public health concern, especially because of its impact on disadvantaged youth. This article examines the role of disadvantage at the family-, peer-, school-, and neighborhood-level, to determine which contexts are related to obesity in adolescence and young adulthood. Methods: We analyzed longitudinal data from Waves I (1994-1995), II (1996), and III (2001-2002) of the National Longitudinal Study of Adolescent Health, a nationally representative population-based sample of adolescents in grades 7-12 in 1995 who were followed into young adulthood. We assessed the relationship between obesity in adolescence and young adulthood, and disadvantage (measured by low parent education in adolescence) at the family-, peer-, school-, and neighborhood-level using multilevel logistic regression. Results: When all levels of disadvantage were modeled simultaneously, school-level disadvantage was significantly associated with obesity in adolescence for males and females and family-level disadvantage was significantly associated with obesity in young adulthood for females. Conclusions: Schools may serve as a primary setting for obesity prevention efforts. Because obesity in adolescence tracks into adulthood, it is important to consider prevention efforts at this stage in the life course, in addition to early childhood, particularly among disadvantaged populations. (Contains 4 tables.)