This report presents an overview of the prevalence, characteristics, morbidity, mortality, and risk factors for noninsulin-dependent diabetes (NIDDM) in Blacks and Whites in the United States. Data are drawn primarily from national surveys, but the report also includes the few clinical studies that have differentiated the two races. NIDDM constitutes 90-95% of all diabetes in the United States and is more prevalent in Black Americans than in Whites. Diabetes prevalence increases with age for both races and reaches 26% among Blacks aged 65-74 years compared with 18% among Whites. Rates of diabetes among persons aged 20-74 years are 30% higher in White women, 70% higher in Black men, and 100% higher in Black women, compared with White men. Approximately half of diabetes is undiagnosed in both races. White and Black diabetics are similar with regard to age, duration of diabetes, and diabetes therapies, although Blacks of both sexes are more obese than their White counterparts. Rates of vision loss, amputations, and renal disease are 1.5-4 times higher in Blacks than in Whites, although prevalence of hypertension is about equal in the two races. Blacks and Whites see the same physician specialists for their diabetes, but Whites have approximately 40% more visits to office-based physicians each year. Diabetes-specific mortality has declined significantly in the past decade and may now be lower in Black than in White diabetics. Risk factors for diabetes, including age, sex, obesity, and family history of diabetes, all operate within both race groups and probably interact with each other. The effect of gender and family history on rates of diabetes is similar in Blacks and Whites. Blacks have higher rates of diabetes at each obesity level, indicating that obesity alone cannot explain the differential in prevalence between the races. Impaired glucose tolerance (IGT), a strong risk factor for development of diabetes, increases with age in all race/sex groups except for Black women older than 54 years in whom rates of IGT decline, possibly because of conversion of IGT to diabetes.