Objectives. Increased platelet activation plays an important role in the development of atherosclerosis. Mean platelet volume (MPV) is a determinant of platelet activation. In our study, we aimed to determine whether MPV levels are elevated in non-dipper patients compared with dippers and healthy controls. In addition, we tried to find out if MPV levels are correlated with blood pressure measurements in hypertensive patients. Methods. This cross-sectional study included 56 hypertensive patients; 27 age- and sex-matched healthy volunteers were enrolled to study as a control subjects. Ambulatory blood pressure monitoring was performed for all patients. Hypertensive patients were divided into two groups: 28 dipper patients (10 male, mean age 51 +/- 8 years) and 28 non-dipper patients (11 male, mean age 53 +/- 10 years). MPV was measured in a blood sample collected in EDTA tubes and was also used for whole blood counts in all patients. Results. In non-dipper patients, 24-h systolic blood pressure (141.5 +/- 10.21 vs 132.3 +/- 7.7 mmHg, p < 0.001), 24-h diastolic blood pressure (88.2 +/- 8.5 vs 81.0 +/- 8.2 mmHg, p < 0.01) and 24-h average blood pressure (105.7 +/- 8.5 vs 97.7 +/- 7.4 mmHg, p < 0.001) are significantly higher than dippers. Whereas daytime measurements were similar between dippers and non-dippers, there was a significant difference between each group during night-time measurements (night-time systolic 137.1 +/- 11.0 vs 120.2 +/- 8.0 mmHg, p < 0.001; night-time diastolic 85.3 +/- 8.0 vs 72.8 +/- 7.9 mmHg, p < 0.001). Non-dipper patients (9.61 +/- 0.42 fl) demonstrated higher levels of MPV compared with dippers (9.24 +/- 0.35 fl) and normotensives (8.87 +/- 0.33 fl) (p < 0.001 and p < 0.001, respectively). There was significant correlation between MPV and ambulatory diastolic and systolic blood pressure in non-dipper hypertensives. Conclusion. Our results suggest that MPV, a determinant of platelet activation, has a positively correlation with blood pressure and elevated in non-dipper compared with dippers and controls. Increased platelet activation could contribute to increase the atherosclerotic risk in non-dipper patients compared with dippers.