In the United States, black women are at much greater risk for obesity than black men. We explored whether adolescent behaviors (family dinners, hours of television, playing sports with mother, playing sports with father, bouts of physical activity) were associated with gender disparity in 6-year obesity incidence in young adulthood. We used data from the nationally representative National Longitudinal Study of Adolescent Health to examine adolescent behaviors in nonimmigrant black (n = 1,503) and white (n = 4,452) youths in 1994-95 (aged 11-19 years) and 1995-96 (aged 12-20). We assessed gender disparity in obesity incidence (female incidence minus male incidence) during young adulthood (2001-02; aged 18-26). Standardized gender disparities were calculated using race- and gender-stratified, covariate-adjusted logistic regression models in which males and females were set to the same distributions of adolescent behaviors. In adolescence, black females reported less leisure-time physical activity and lower likelihood of playing sports with either parent compared with black males. Setting adolescent behaviors equal for black males and females did not reduce the estimated gender disparity in obesity incidence (nonstandardized: 9.8 percentage points (95% confidence interval (CI): 4.5, 15.1); fully standardized: 10.2 percentage points (5.2, 15.2)). There was little gender disparity in whites before or after adjustments. To our knowledge, this is the first study to examine to what extent behavioral differences during adolescence might account for gender disparity in obesity incidence in black young adults. Male-female differences in these adolescent behaviors did not appear to underlie the gender gap in young adult obesity.