About 1 third of all patients with essential hypertension reveal an impaired circadian pattern of blood pressure. This phenomenon called "non-dipping" (i.e. a lack of the normal nocturnal fall in blood pressure) is related to a higher incidence of end-organ damage such as left ventricular hypertrophy. It is the purpose of this study to evaluate, whether or not non-dipping of blood pressure may worsen the prognosis of hypertensive subjects. 116 consecutive hypertensives underwent an ambulatory blood pressure monitoring (ABPM) using the Spacelabs 2000 device. 2 groups were established: Group I (n = 87) were "dippers", group II (n = 29) "non-dippers" showing a diminished or even lack of nocturnal fall in blood pressure. No difference was seen concerning sex, mean 24-hour systolic blood pressure, systolic and diastolic causal blood pressure and heart rate. However, a significant difference in age and mean 24-hour diastolic blood pressure could be observed. In a follow-up investigation after approximately 31 months all patients and/or their physicians were contacted concerning cardiovascular events during the time since the ABPM was performed. In Group I only 1 transient ischemic attack occurred, but in group II 4 patients showed major cardiovascular events: 3 deaths occurred (2 of which caused by myocardial infarction, 1 by apoplexy), while 1 suffered from a transient ischemic attack (p < 0.001). Thus, in essential hypertension non-dipping of blood pressure is associated with an increased occurrence of cardiovascular events, and, therefore, the circadian blood pressure profile should be carefully monitored.