In the past two decades, techniques for the measurement of blood pressure outside the medical setting have unmasked highly prevalent situations. A significant proportion of patients with office blood pressure levels above the thresholds for diagnosing hypertension or above the limits where those being treated are considered to be adequately controlled actually show normal ambulatory blood pressure levels. These patients have white-coat hypertension if untreated or false resistance to antihypertensive therapy because of the white-coat effect if treated. However, some individuals with normal office blood pressure measurements show elevated ambulatory blood pressure levels, and thus have masked hypertension if untreated or masked uncontrolled hypertension if treated. When looking for white-coat hypertension in patients with elevated office blood pressure levels or when looking for masked hypertension in office-controlled patients, up to one in three patients in each scenario would have white-coat or masked hypertension. Although related clinical factors, such as age, gender and global cardiovascular risk, are associated with both conditions, their abilities to predict such a misclassification are very low. Thus, assessing individual blood pressure levels by means of an ambulatory technique, particularly ambulatory blood pressure monitoring, is now considered a priority in diagnosing hypertension and in evaluating hypertension control.