It is frequently stated that the risk of sequelae from hypertension at a given level of severity is higher among blacks than whites, although little empirical evidence supports that supposition. In this work we examined the basis for accepting the existence of a black: white differential in hypertension outcomes in a representative biracial sample of the U.S. population followed in the First National Health and Nutrition Examination Survey (NHANES-1) Epidemiologic Follow-up Study. As well recognized, the risk associated with increasing blood pressure is not dichotomous but varies across the entire distribution in a curvilinear fashion. The rightward skew of the blood pressure distribution with increasing mean levels affects comparisons between populations, since the change in shape results in a change in the mix of case severity. These considerations can influence estimates of the relative population-attributable risk from hypertension, considered as a dichotomous classification in blacks and whites. Although the relative risk of death associated with a systolic blood pressure of > or = 140 mmHg in this study was higher for blacks than for whites (1.7 and 1.5, respectively), with all-cause mortality as the outcome, the logistic coefficient for systolic blood pressure was not significantly different among white as compared with black men (beta = 0.016 vs. 0.010; p = 0.320 for race interaction term) and was slightly greater among white vs. black women (beta = 0.013 vs. 0.010; P = 0.05). After strata-specific blood pressure adjustment, the principal determinant of increased population risk for both black men and women was the higher prevalence of hypertension, not differential severity. The population-attributable risk for hypertension was at least two times higher among blacks because of the higher prevalence among them; moreover, the increased prevalence accounted for 10% of the interethnic difference in mortality. Data from this study indicate that hypertension was not more severe among individual blacks, simply more common in the population.