Data are sparse regarding hypertension prevalence, treatment, and control among some ethnic groups of American women. Furthermore, the effects of ethnicity on hypertension, independent of other factors that vary with ethnicity, are poorly understood. We examined the prevalence of hypertension (defined as systolic > or =140 or diastolic > or =90 mm Hg or receiving treatment), treatment, and control (to <140/<90 mm Hg) in a multiethnic study of premenopausal and perimenopausal women. Stepwise multivariable logistic regression was used to select covariates associated with hypertension. Among 3292 women, 46.9% were white, 28.3% were black, 8.7% were Hispanic, 7.6% were Chinese, and 8.5% were Japanese. Among these 5 ethnic groups, respectively, there was substantial variation in prevalence of normal blood pressure levels (<120/<80 mm Hg; 59.9%, 35.4%, 16.8%, 67.2%, and 63.7%) and hypertension (14.5%, 38.1%, 27.6%, 12.8%, and 11.0%). After multivariable adjustment, hypertension prevalence was 2 to 3x higher among black and Hispanic women but similar among Chinese and Japanese women compared with white women. Among hypertensive participants, prevalence of antihypertensive treatment was highest among blacks (58.9%) and whites (55.2%) and lowest among Chinese (34.4%). Prevalence of control to goal blood pressure levels was highest among whites (43.0%) and Japanese (38.7%) and markedly lower among Hispanic women (11.4%). Compared with whites, black and Hispanic women have significantly higher prevalence of hypertension independent of other factors, whereas Chinese and Japanese women have similar prevalence. Treatment and control rates vary considerably across ethnicities. Greater efforts must be made to improve hypertension awareness, treatment, and control in all middle-aged women, particularly those in ethnic minority groups.