BACKGROUND: Our aim was to assess how the population-attributable fraction (PAF) for premature mortality due to cardiovascular disease (CVD) associated with hypertension changes if blood pressure (BP) thresholds for hypertension were lowered from systolic/diastolic BP ≥140/90 mm Hg to ≥130/80 mm Hg, as defined using the 2017 American College of Cardiology/American Heart Association blood pressure guideline. METHODS: Analyses were conducted using a database of participants who underwent a national health checkup examination started in 2008 in Japan (n = 510,238; mean age, 59.6 ± 8.1 years; 42% men). Each participant was categorized as having normal or elevated BP, or stage 1 or 2 hypertension according to the guideline. Data on premature mortality due to CVD occurring before age 70 years were available through March 2015. RESULTS: Over a median follow-up of 3.4 years, 739 deaths from CVD occurred. After multivariable adjustment, hazard ratios for premature CVD mortality for elevated BP, stage 1 hypertension, and stage 2 hypertension vs. normal BP were 1.02 (95% confidence interval, 0.72, 1.44), 1.33 (1.02, 1.75), and 2.41 (1.90, 3.05), respectively. The PAF associated with stage 1 and 2 hypertension was 4.4% and 39.4%, respectively. CONCLUSIONS: In the current nationwide study of Japanese adults, stage 1 and 2 hypertension were associated with an increased risk for premature CVD mortality. The PAF for premature CVD mortality associated with hypertension increased by 4.4% if BP thresholds for hypertension were lowered from systolic/diastolic BP ≥140/90 to ≥130/80 mm Hg.