Compared with non-Hispanic whites, Mexican Americans have a higher prevalence of diabetes, greater adiposity, and an unfavorable body fat distribution. The prevalence of hypertension, however, is similar or lower in Mexican Americans than in non-Hispanic whites. There is little information on the level of blood pressure control in Mexican Americans. We compared the mean blood pressure levels of Mexican American and non-Hispanic white hypertensive subjects in the San Antonio Heart Study, a population-based study of diabetes and cardiovascular disease. Hypertension was defined as one or more of a systolic blood pressure > or = 160 mm Hg, a diastolic blood pressure > or = 95 mm Hg, and current use of antihypertensive medications. Three hundred and fifty-eight Mexican Americans and 241 non-Hispanic whites met these criteria. Poor hypertension control was defined as a systolic blood pressure > or = 160, a diastolic blood pressure > or = 95 mm Hg, or both. After adjustment for age, gender, obesity, body fat distribution, and level of educational attainment, Mexican American hypertensive subjects were in significantly poorer control than non-Hispanic white hypertensive subjects. The reasons for their poorer control are unknown, but our findings emphasize the importance of hypertension in this ethnic group.