We investigated factors underlying discrepancy between screening blood pressure and daytime ambulatory blood pressure (the difference) in a community-based population in northeastern Japan. Screening and ambulatory pressures were measured in 706 untreated subjects aged 20 yr or older. We analyzed the effects of age and blood pressure on the difference and then performed multivariate stepwise linear regression analysis using the difference as the dependent variable. The systolic difference positively correlated with age in men. Women in their 40s exhibited a large difference, disturbing the linear relationship between the difference and age. The difference positively correlated with the screening pressure in men and women. A positive difference (screening pressure > ambulatory pressure) was observed at screening pressures above 130/75 mmHg. The difference inversely correlated with the ambulatory pressure. Multivariate analysis demonstrated that body mass index and male sex were positively associated with the systolic and diastolic blood pressure differences. The daytime pulse rate was negatively associated with the systolic difference, and the standard deviation of daytime diastolic ambulatory blood pressure was positively associated with the diastolic difference. The diastolic difference in subjects with isolated systolic hypertension based on the screening pressure was significantly smaller than that in subjects with systolic/diastolic hypertension. The difference in subjects with isolated systolic hypertension based on ambulatory pressure was significantly higher than that in systolic/diastolic hypertension. When white-coal (isolated screening) hypertension was defined as a screening systolic pressure > or = 140 mmHg, a diastolic pressure > or = 90 mmHg, or both, and a 24-h ambulatory pressure < 136/87 mmHg in men and < 131/86 mmHg in women, white-coat (isolated screening) hypertension was present in 79 (56.8%) of 139 subjects with screening hypertension. The results confirm that the discrepancy between screening and ambulatory blood pressure is due to a variety of factors, including age, sex, blood pressure levels, and baroreflex function. Our results indicate that screening blood pressure in elderly hypertensive patients should be evaluated carefully.