Arterial blood pressure circadian rhythm: significance and clinical implications Arterial blood pressure exhibits a circadian rhythm characterized by a decrease during the sleep period and a steep increase in the early morning hours that can be characterized by 24 h ambulatory blood pressure monitoring (ABPM). The absence of a nocturnal dipping or an excessive morning surge, commonly observed in hypertensive patients, is associated with an increased cardiovascular and renal risk. Numerous studies show that a better control of nocturnal blood pressure can be obtained by the administration of anti-hypertensive medication at the evening time, improving microalbuminuria, left heart hypertrophy, or arterial intima-media thickness, but only one study has so far demonstrated a decrease of major cardiovascular events. In this context, the decision on restoring or not the nocturnal dipping should be left to the judgement of the clinician, and applied in an individual manner to each patient.