To assess the relationship between ethnicity and hypertension using individual admixture and blood pressure measurements, we performed a cross-sectional study of African American and Hispanic American (HA) women enrolled in the Women's Health Initiative. The admixture odds ratio for systolic and diastolic hypertensive risk was determined using linear regression models in which the proportional measurements of European (EUR), sub-Saharan African (AFR) and Amerindian (AMI) admixture was analyzed using ancestry informative markers. In both African-American women (n=10,147) and HA women (n=4908) there was a significant positive association between hypertension and African admixture (P<10(-4)). This relationship was observed for both systolic and diastolic hypertension examined as a continuous or dichotomous trait, and whether age, body mass index, years since menopause and a measurement of socioeconomic status were used as covariates. The odds ratio associated with AFR admixture in a dichotomous model of hypertension was 3.06 (95% confidence interval 2.72-3.45). AMI admixture was associated with lower odds of hypertension and appeared to be more protective, relative to EUR admixture. These data show that African admixture increases the risk for hypertension and provide additional support for evaluating therapeutic efficacy and conducting genetic analyses of hypertension in different ethnic groups.