Patients with hypertension have evidence of platelet activation. Mean platelet volume (MPV), an indicator of platelet activation has been shown to be elevated in patients with hypertension. Prehypertension is also associated with an increase in cardiovascular morbidity and mortality. The aim of this study was to assess the MPV in patients with prehypertension and hypertension. This study included newly diagnosed and untreated 87 prehypertensive patients, 30 hypertensive patients and 35 normotensive control subjects matched for age, gender, and body mass index. All patients and controls gave informed consent. The MPV values of patients with prehypertension and hypertension were significantly higher than those of the control group (8.4 +/- 0.8 and 8.8 +/- 0.7 versus 7.9 +/- 0.5 fl; p < 0.05 and p < 0.001 respectively). It was also higher in hypertensives than in prehypertensives (8.8 +/- 0.7 versus 8.4 +/- 0.8 fl; p < 0.05). However, we found that the presence of the hypertension (beta = 0.28, P = 0.003) was only significant predictors of higher MPV in a multivariable model that adjusted for other variables. We have shown that, MPV, an indicator of platelet activation was significantly higher in patients with prehypertension and hypertension when compared with control subjects. We have also showed that MPV was also higher in patients with hypertension than in patients with prehypertension. However, presence of the hypertension was only significant predictor of higher MPV.