Casual (or office) blood pressure values have been shown to be associated with cardiovascular morbidity or mortality in a variety of prospective trials assessing cardiovascular risk. In recent years, however, controversies have developed regarding the capacity of casual blood pressures to predict cardiovascular risk in an individual patient with high blood pressure. Prospective, cross-sectional studies have been performed in several centres that compare the capacity to predict hypertensive target organ involvement by casual vs 24-h mean, awake, or sleep blood pressures. Ambulatory blood pressure has been consistently superior to casual blood pressure in predicting target organ involvement in hypertension. As most of the data collected to date has involved cardiac studies, however, fewer conclusions can be drawn regarding renal and cerebrovascular disease. With regard to cardiac structure and/or function, ambulatory blood pressure is much more useful than casual blood pressure in determining the likelihood of an abnormal index in an individual patient with hypertension.