The development and clinical application of ambulatory blood pressure monitoring (ABP M) has brought several of the main features of the circadian blood pressure (BP) rhythm to light. ABP M has shown to be a very useful method in cardiovascular risk assessment and remains the only method of diagnosing a non-dipping blood pressure profile. A 'non-dipping' BP profile is currently regarded as a risk factor in its own right for cardiovascular (CV) events and target organ damage. Nevertheless, the reliability of ABP M in assessing dipping status is still being questioned. Furthermore, a clear-cut definition of 'non-dipping' has not been established so far. The pathophysiological mechanism(s) of a non-dipping profile might involve abnormalities in extracellular volume and/or vascular resistance regulation. In addition, differences in daytime and nighttime activity, sleep quality and body position during sleep are involved as well. A reduction in cardiovascular risk by a pharmacologically induced switch from a non-dipper to a dipper status might be expected, but remains to be proven.