BACKGROUND AND OBJECTIVES: A non-dipping pattern in hypertensive patients has been shown to be associated with a greater left ventricular (LV) hypertrophy, LV diastolic impairments and prolonged ventricular repolarization. The dynamic parameters of the QT dispersion (QTd) have been highlighted as markers of ventricular repolarization heterogeneity. The aim of this study was to demonstrate if the extent of nocturnal blood pressure (BP) fall was related to the LV mass, LV diastolic function and dynamic parameters of the QTd. SUBJECTS AND METHODS: 122 subjects, receiving electrocardiography, 24-hour ambulatory BP monitoring, 12 lead-24hr Holter monitoring and 2-dimensional Doppler echocardiography examinations, were enrolled. The subjects were classified as normotensive, dipper and non-dipper. The LV mass (LVM) and LV diastolic indices were measured. Using the QT Guard software, with 12 lead-24hr Holter monitoring, the QTd, mean QTd, QTd variation (the difference between the maximum minus the minimum QTd value observed over the recording time), QTd maximum (the maximum difference of QTd between consecutive beats) and QTd variability (QTd standard deviation) were analyzed. RESULTS: Of the 122 patients, 39 and 40 were placed in the dipper and non-dipper groups, respectively. The non-dipper group had a greater LVM index (LVMI) than the dipper group (p<0.01). The non-dipper group had greater increases in their A velocity (p<0.01), and more prolonged deceleration (p<0.01) and isovolumic relaxation (p<0.01) times than the dipper group. There were no significant differences in the QT and QTc interval between the 3 groups, but the QTd was much more increased in the non-dipper than the dipper and normotensive groups (p<0.01). For the dynamic parameters of the QTd, the QTd variation, QTd maximum and QTd variability were significantly increased in the non-dipper compared to the dipper and normotensive groups (p<0.05). Comparing the dipper and normotensive groups, there were no significant differences in the LVMI, LV diastolic indices, QTd and dynamic parameters of the QTd. CONCLUSION: The non-dipper group of hypertensive patients had a greater LVMI, more impaired LV diastolic function and greater increases in their QTd and dynamic parameters of the QTd compared to the dipper and normotensive groups, suggesting the possibility of a much greater chance of cardiovascular events, and their complications, in the non-dipper compared to the dipper group.