Prehypertension is associated with increased risk for hypertension and cardiovascular disease. Data are limited on the temporal changes in the prevalence of prehypertension and risk factors for hypertension and cardiovascular disease among US adults with prehypertension. We analyzed data from 30 958 US adults ≥20 years of age who participated in the National Health and Nutrition Examination Surveys between 1999 and 2012. Using the mean of 3 blood pressure (BP) measurements from a study examination, prehypertension was defined as systolic BP of 120 to 139 mm Hg and diastolic BP <90 mm Hg or diastolic BP of 80 to 89 mm Hg and systolic BP <140 mm Hg among participants not taking antihypertensive medication. Between 1999–2000 and 2011–2012, the percentage of US adults with prehypertension decreased from 31.2% to 28.2% ( P trend=0.007). During this time period, the prevalence of several risk factors for cardiovascular disease and incident hypertension increased among US adults with prehypertension, including prediabetes (9.6% to 21.6%), diabetes mellitus (6.0% to 8.5%), overweight (33.5% to 37.3%), and obesity (30.6% to 35.2%). There was a nonstatistically significant increase in no weekly leisure-time physical activity (40.0% to 43.9%). Also, the prevalence of adhering to the Dietary Approaches to Stop Hypertension eating pattern decreased (18.4% to 11.9%). In contrast, there was a nonstatistically significant decline in current smoking (25.9% to 23.2%). In conclusion, the prevalence of prehypertension has decreased modestly since 1999–2000. Population-level approaches directed at adults with prehypertension are needed to improve risk factors to prevent hypertension and cardiovascular disease.