BACKGROUND: Prehypertension is common and is associated with increased vascular mortality. The extent to which it increases risk of nonfatal myocardial infarction, stroke, and congestive heart failure is less clear. METHODS AND RESULTS: We determined the prevalence of prehypertension, its association with other coronary risk factors, and the risk for incident cardiovascular disease events in 60,785 postmenopausal women during 7.7 years of follow-up using Cox regression models that included covariates as time-dependent variables. Prehypertension was present at baseline in 39.5%, 32.1%, 42.6%, 38.7%, and 40.3% of white, black, Hispanic, American Indian, and Asian women, respectively (P<0.0001 across ethnic groups). Age, body mass index, and prevalence of diabetes mellitus and hypercholesterolemia increased across blood pressure categories, whereas smoking decreased (all P<0.0001). Compared with normotensive women (referent), adjusted hazard ratios for women with prehypertension were 1.58 (95% confidence interval [CI], 1.12 to 2.21) for cardiovascular death, 1.76 (95% CI, 1.40 to 2.22) for myocardial infarction, 1.93 (95% CI, 1.49 to 2.50) for stroke, 1.36 (95% CI, 1.05 to 1.77) for hospitalized heart failure, and 1.66 (95% CI, 1.44 to 1.92) for any cardiovascular event. Hazard ratios for the composite outcome with prehypertension did not differ between ethnic groups (P=0.71 for interaction), although the numbers of events among Hispanic and Asian women were small. CONCLUSIONS: Prehypertension is common and was associated with increased risk of myocardial infarction, stroke, heart failure, and cardiovascular death in white and nonwhite postmenopausal women. Risk factor clustering was conspicuous, emphasizing the need for trials evaluating the efficacy of global cardiovascular risk reduction through primordial prevention.