BACKGROUND The independent prognostic value of blood pressure (BP) variability in treated hypertension is not yet clear. We investigated the relationship between BP variability, evaluated by noninvasive monitoring, and cardiovascular outcome in treated hypertensive patients. METHODS The occurrence of fatal and nonfatal cardiovascular events was evaluated in 1472 treated patients. Subjects with the standard deviation of daytime or night-time systolic BP below or above the median of the population were classified as having low or high BP variability. Specifically, 738 and 734 patients had low and high daytime BP variability, respectively, and 739 and 733 subjects had low and high night-time BP variability, respectively. RESULTS During follow-up (4.88 +/- 2.9 years, range 0.2-11.6 years) there were 119 events. The event rates per 100 patient-years in subjects with low and high BP variability according to daytime BP were 1.18 and 2.01, respectively, and in those with low and high BP variability according to night-time BP were 1.2 and 2.05, respectively. Event-free survival was significantly different between the low and high BP variability groups (P = .006 for both daytime and night-time BP). However, after adjustment for other covariates in a Cox multivariate analysis, the adverse prognostic relevance of high BP variability was no longer detectable, whereas age, smoking habit, LDL cholesterol, diabetes, previous events, LV hypertrophy, and daytime or night-time systolic BP resulted independent predictors of risk. CONCLUSIONS Increased BP variability is associated with higher incidence of cardiovascular events, but also with other relevant prognostic factors. Indeed, in multivariate analysis the possible adverse prognostic impact of BP variability is no longer evident. Thus, in treated hypertension, BP variability evaluated by noninvasive monitoring is not an independent predictor of outcome.