We sought to investigate the prognosis in subjects with "white-coat" hypertension (WCHT) and "masked" hypertension (MHT), in which blood pressure (BP) is lower in clinical measurements than during ambulatory monitoring. The prognostic significance of WCHT remains controversial, and little is known about MHT. We obtained 24-h ambulatory BP and "casual" BP (i.e., obtained in clinical scenarios) values from 1,332 subjects (872 women, 460 men) > or =40 years old in a representative sample of the general population of a Japanese community. Survival and stroke morbidity were then followed up for a mean duration of 10 years. Composite risk of cardiovascular mortality and stroke morbidity examined using a Cox proportional hazards regression model for subjects with WCHT (casual BP > or =140/90 mm Hg, daytime BP <135/85 mm Hg; relative hazards [RH])1.28; 95% confidence interval [CI] 0.76 to 2.14) was no different from risk for subjects with sustained normal BP (casual BP <140/90 mm Hg, daytime BP <135/85 mm Hg). However, risk was significantly higher for subjects with MHT (casual BP <140/90 mm Hg, daytime BP > or =135/85 mm Hg; RH 2.13; 95% CI 1.38 to 3.29) or sustained hypertension (casual BP > or =140/90 mm Hg, daytime BP > or =135/85 mm Hg; RH 2.26; 95% CI 1.49 to 3.41) than for subjects with sustained normal BP. Similar findings were observed for cardiovascular mortality and stroke morbidity among subgroups by gender, use of antihypertensive medication, and risk factor level (all p for heterogeneity >0.2). Conventional BP measurements may not identify some individuals at high or low risk, but these people may be identifiable by the use of ambulatory BP.