To determine whether the higher rate of hospitalization among African Americans for congestive heart failure (CHF) could be explained by racial differences in the prevalence of clinical risk factors for CHF.Retrospective cohort study.A large health maintenance organization (HMO).A sample of 64,877 enrollees (27% African American and 73% white) of the Northern California Kaiser Permanente Medical Care Program who took at least one multiphasic health checkup (MHC) at or after the age of 40 years and were free of CHF at that time.First hospitalization with a principal diagnosis of CHF.Among cohort members younger than 60 years at baseline MHC, the age-adjusted risk ratio (RR) (African American/white) for CHF hospitalization was 2.14 for men and 2.73 for women, while for persons 60 years of age and older at MHC, the age-adjusted RR was 1.48 for both sexes. Cox proportional hazards models were used to adjust for risk factors and length of follow-up. In persons aged 60 years and older, the race difference was explained by greater prevalence of hypertension and diabetes in African Americans (RR = 1.12; 95% confidence interval [CI], 0.94 to 1.34 after adjustment for hypertension and diabetes). In those younger than 60 years, findings differed by sex. For men, African-American race was no longer a significant predictor of CHF after adjusting for hypertension, diabetes, left ventricular hypertrophy on electrocardiogram, and body mass index (adjusted RR = 1.16; 95% CI, 0.86 to 1.56). However, among younger women, African Americans continued at increased risk despite adjustment for these variables as well as smoking, plasma cholesterol, renal function, alcohol use, and myocardial infarction (adjusted RR = 1.49; 95% CI, 1.00 to 2.21).In this HMO population, the race differences in first hospitalization for CHF are largely explained by known clinical and behavioral risk factors, although in younger women these risk factors do not completely explain the excess risk among African Americans. These findings highlight the role of hypertension and diabetes in the development of CHF, particularly among African Americans.