The interest of chronotherapy in the field of arterial hypertension is progressively rising, especially in treated hypertensive patients characterized by a small decrease of their blood pressure during the night, and therefore often presenting a high cardiovascular risk. There are more and more data showing that administration of one antihypertensive drug in the evening (and even aspirin) can improve the blood pressure control during the night and the day/night blood pressure pattern, and so can diminish the level of risk. The role of chronotherapy also emphasizes the interest of 24 h ambulatory blood pressure monitoring in the management of high risk hypertensive patients.