The aim of this study was to quantify the contributions of socioeconomic, psychosocial, behavioral, reproductive, and neighborhood exposures in young adulthood to Black-White differences in incident obesity. In the Coronary Artery Risk Development in Young Adults (CARDIA) study, 4488 Black or White adults aged 18 to 30 years without obesity at baseline (1985-1986) were followed over 30 years. Sex-specific Cox proportional hazard models were used to estimate Black-White differences in incident obesity. Models were adjusted for baseline and time-updated indicators. During follow-up, 1777 participants developed obesity. Black women were 1.87 (95% CI: 1.63-2.13) times more likely and Black men were 1.53 (95% CI: 1.32-1.77) times more likely to develop obesity than their White counterparts after adjusting for age, field center, and baseline BMI. Baseline exposures explained 43% of this difference in women and 52% in men. Time-updated exposures explained more of the racial difference in women but less for men, compared with baseline exposures. Adjusting for these exposures accounted for a substantial but incomplete proportion of racial disparities in incident obesity. Remaining differences may be explained by incomplete capture of the most salient aspects of these exposures or potential variation in the impact of these exposures on obesity by race.