Background: In the United States, Black women are at much greater risk for obesity than Black men. Little is known about the factors underlying this disparity. Objectives: We explored whether, in U.S. Black young adults, childhood sociodemographic factors (parental education, single-mother household, number of siblings, number of minors in household, birth order, and female caregiver's age) and adolescent behaviors (family dinners, hours of television, playing sports with mother, playing sports with father, bouts of physical activity) were associated with gender disparities in obesity. Methods: Analysis datasets were constructed from the nationally representative National Longitudinal Study of Adolescent Health. The datasets included non-immigrant Black and White youths aged 11 to 19 years in 1994-95. Childhood sociodemographic factors (n=7,747) were assessed in 1994-95. Adolescent behaviors (n=5,955) were assessed in 1994-95 and 1995-96. Obesity was measured in 1995-96 and again in 2001-02. For each assessed childhood sociodemographic factor, we evaluated whether the factor modified the female-male prevalence difference. Second, we evaluated whether standardizing Black males and females to the same distributions of the adolescent behaviors reduced the size of the predicted gender disparity in young Blacks. Results: In unadjusted and multivariable-adjusted models, parental education consistently modified Blacks' gender disparity (p=0.01). The gender gap was largest at low parental education (16.7% men obese vs. 45.4% women obese) and smallest at high parental education (28.5% men obese vs. 31.4% women obese). In Whites, there was little overall gender difference in obesity prevalence. Blacks females reported less leisure-time physical activity and lower likelihood of sport with either parent than did Black males. Standardizing by these behaviors did not reduce the predicted gender disparity in obesity incidence. Discussion: Black young adults' gender disparity in obesity prevalence was concentrated in families with low parental education. Male-female differences in the adolescent behaviors examined did not appear to underlie the obesity gender gap in young U.S. Blacks. Future research should investigate environmental, physiologic, and behavioral factors related to the differential regulation of energy balance in young Black males and females.