Blood pressure variability (BPV) is a classical physiological phenomenon. This paper describes major epidemiological and clinical issues of BPV which may be important to understand the background of this interesting feature. In healthy subjects, BPV is a measure of hemodynamic condition and refl ects function of autonomic nervous system. BP fl uctuations result from the complex interaction between environmental stimulation, genetic factors and cardiovascular control mechanisms. Abnormal BPV is recognized in persons with a blurred dipping pattern (i.e. extreme dipping, non-dipping, reverse-dipping, morning surge of BP) or increased variations of day-time or night-time BP (high BP lability). Inappropriate BPV worsens the outcome, including increase in all-cause and cardiac mortality and incidence of cardiovascular events, and advance in target organ damage. Abnormal BPV may be softened or removed with suitable time-dependent administration of anti-hypertensive agents, especially those acting on the renin-angiotensin system.