Ambulatory blood-pressure monitoring (ABPM) is the best method to identify causal blood-pressure increases, and for differentiating between white-coat (office) blood pressure and sustained hypertension. This differentiation is necessary because 20% of patients with mild hypertension (90-104 mmHg diastolic, without end-organ damage) have white-coat hypertension. Thus, using conventional blood-pressure measurements (repeated measurements on at least two different occasions) for diagnosing mild hypertension (85% of all hypertensives!) many persons will be overtreated. The results of intervention in mild hypertension will improve through a better identification of patients at risk. ABPM correlates best with end-organ damage. The introduction of ABPM for diagnosing mild hypertension seems to be the best way to differentiate between white-coat hypertension without increased cardiovascular risk and sustained hypertension with increased cardiovascular risk. This procedure allows a better treatment of patients at risk and it avoids overtreatment. The ABPM diastolic blood-pressure range for mild hypertension is 85-92 mmHg (mean values during the active phase).