We sought to estimate the prevalence of hypertension and characteristics of hypertensive adults in the United States according to blood pressure (BP) thresholds used for diagnosis and estimate their associated cardiovascular disease risk. Analyses included adults 20 years of age or older in the 2013 to 2014 National Health and Nutrition Examination Survey (N=5389) and enrolled participants in SPRINT (Systolic Blood Pressure Intervention Trial; N=9361) and the ACCORD-BP trial (Action to Control Cardiovascular Risk in Diabetes-Blood Pressure; N=4733). In the National Health and Nutrition Examination Survey, prevalence estimates incorporated the probability of observing elevated BP on 2 separate occasions. Using the new BP thresholds of ≥130/80 mm Hg, ≈24 million new American adults would be diagnosed as having hypertension and 4.3 million would be recommended to start antihypertensive medications. These individuals would have a lower mean atherosclerotic cardiovascular disease risk (17%) than participants in SPRINT and ACCORD-BP (22% and 27%) and would be less likely to have prevalent cardiovascular disease (9% versus 17% and 34%). In SPRINT and ACCORD-BP, only a minority (9% and 13%) of participants were not on antihypertensive medications at baseline, and rates of incident cardiovascular disease in these participants were substantially lower compared with those on baseline BP medications. We conclude that adopting the American College of Cardiology/American Heart Association guidelines would lead to a substantial increase in the prevalence of hypertension and in the number of American adults recommended to start antihypertensive medications. These individuals would have a substantially lower cardiovascular risk than most participants previously studied in 2 large BP trials.