The diurnal rhythm of blood pressure (BP) is influenced by both extrinsic and intrinsic factors, with the former usually being of greater significance. Non-dippers, in whom the normal nocturnal fall of pressure is diminished, have been reported to show more target organ damage (left ventricular hypertrophy (LVH)) than dippers, which may be explained by a higher average 24 h BP. Whether or not the pattern of BP (as opposed to the level) also is prognostically important is probable but unproven, given the known morning surge of the incidence of many acute cardiovascular events. The pathological significance of different diurnal patterns of BP change may depend both on the method of analysis and on the outcome measure used.