Measurements of ambulatory blood pressure as an adjunct to casual/clinic blood pressure measurements are currently widely used for the diagnosis and treatment of hypertension. There have been many recent reports on the clinical significance of ambulatory blood pressure. The relationship between ambulatory blood pressure level and target-organ damage uniformly demonstrated on a cross-sectional basis that average ambulatory blood pressure is correlated to target-organ damage. The main limitation of cross-sectional studies, however, is the difficulty of drawing inferences about causality from them. We have been monitoring the prognosis of the Ohasama population and reported that ambulatory blood pressure is superior to casual blood pressure for the prediction of mortality. We also observed that the daytime ambulatory blood pressure is a better predictor for cardiovascular mortality in the general population than is the night-time ambulatory blood pressure. It is widely recognized that casual/clinic blood pressure is less representative of the true blood pressure level than is average ambulatory blood pressure. One reason that clinic blood pressure is a poor predictor of prognosis is that clinic blood pressure includes several biases, including the white-coat effect. For determining white-coat hypertension, measurement of blood pressure in a non-medical setting such as ambulatory blood pressure monitoring is indispensable. We examined the prognostic significance for mortality of white-coat hypertension and reversed white-coat hypertension (clinic blood pressure <ambulatory blood pressure). The relative hazard (RH) for the overall mortality for patients with white-coat hypertension was significantly lower than that for true hypertension. Short-term variability of blood pressure has recently attracted attention as a cause of target-organ damage and cardiovascular complications. The findings in cross-sectional studies on the effect of short-term variability of blood pressure are controversial. We observed that short-term variability of blood pressure (variability of blood pressure every 30 min) was independently associated with cardiovascular morbidity. Circadian variation of blood pressure is characterized by a diurnal elevation and a nocturnal decline in blood pressure. In several pathophysiological conditions, however, this nocturnal decline is diminished (non-dipping) and sometimes inverts to nocturnal elevation (inverted dipping). We compared morbidities from strokes for dippers and non-dippers in Ohasama. The incidence of strokes increased with increasing duration of observation for dippers with antihypertensive medication but not in non-dippers with antihypertensive medication. On the other hand, the RH for mortality from cardiovascular diseases increased for non-dippers and inverted dippers. The results suggest that there is a cause-and-effect relationship for dippers and non-dippers. This review demonstrates the independent association between the prognosis of hypertension and each component of ambulatory blood pressure, indicating the prognostic significance of ambulatory blood pressure monitoring.