Estimates of the prevalence of hypertension in the United States have varied owing to differences in interpretation and extrapolation of the data. In 1978 the National High Blood Pressure Education Program issued a consensus document estimating the prevalence of high blood pressure in the United States. Results from the 1976-1980 National Health and Nutrition Examination Survey (NHANES II) allow for a revised estimate. The purpose of this report was to arrive at consensus on a prevalence figure and also to provide information on the distribution of hypertension by blood pressure level, age, race, and sex. The prevalence estimates used are based on hypertension defined as blood pressure measurements greater than or equal to 140/90 mm Hg (average of 3 readings taken on 1 occasion) or self-reported taking of antihypertensive medication. Based on NHANES II data, blacks have a higher prevalence than whites (38% vs 29%) and men show a higher prevalence than women (33% vs 27%). These data again confirm the tendency for the prevalence of hypertension to increase with age in the U.S. population--this holds true for blacks, whites, men, and women. Progress in high blood pressure control efforts has traditionally been measured by changes in the status of awareness, treatment, and control. Changing the hypertension threshold from 160/95 to 140/90 mm Hg, as recently recommended, substantially lowers these measures: the percentage of hypertensives aware of their condition falls from 74% to 54%, the percentage taking antihypertensive medication falls from 56% to 33%, and the percentage with controlled hypertension decreases from 34% to 11%. These apparent decreases reflect a change in the frame of reference rather than changes in hypertension treatment status. In addition, hypertension prevalence rates from NHANES II (1976-1980) were applied to 1983 Bureau of the Census population figures to estimate the total number of Americans with hypertension and their distribution by age, sex, race, and severity of blood pressure level. Since NHANES II did not include persons 75 years of age or older in its sample, data from a pilot study on systolic hypertension in the elderly were used for prevalence estimates in this age group. Estimates for children under 6 years of age and hypertensive persons controlling their pressures without medication could not be included in this analysis because of a lack of reliable data on these groups.