Although the prevalence of obesity in US women is well-described, data are limited on the incidence of major weight gain and obesity. We used data from the First National Health and Nutrition Examination Survey Epidemiologic Follow-up Study to estimate the 10-y incidence of major weight gain (greater than or equal to 10 kg) and obesity [body mass index (BMI, in kg/m2) greater than or equal to 29] in a cohort of US women aged 30-55 y (n = 535 blacks and 2976 whites). In women not obese at baseline, blacks were 60% more likely to become obese than whites [incidence in blacks = 15.5%, 95% confidence interval (CI) = 11.2-19.7; incidence in whites = 9.7%, 95% CI = 8.6-10.8]. This higher incidence of obesity in blacks was largely due to their higher average BMI at baseline. The incidence of major weight gain was 50% higher in blacks than in whites (in blacks, 17.3%; 95% CI = 13.6-21.0; in whites, 11.7%; 95% CI = 10.3-13.1). We estimate that in black and white women, respectively, 16% and 12% of coronary heart disease is attributed to major weight gain whereas 35% and 21% is attributed to being obese.