Platelets may be activated in hypertension (HT). Hypertensive crisis is an extreme phenotype of HT and HT-related thrombotic complications. We aimed to assess mean platelet volume (MPV) in patients with hypertensive crises. This study included 215 hypertensive urgency (HU) patients (84 male, mean age 66 +/- 15 years) and 60 hypertensive emergency (HE) patients (26 male, mean age 68 +/- 13 years), who were admitted to the emergency department with a diagnosis of hypertensive crises. Control group was composed of age-and sex-matched 39 normotensive patients. Blood samples were withdrawn for whole blood count and routine biochemical tests. Systolic blood pressure (BP) was significantly higher in the HE group than in the HU group (p<0.001). Median mean platelet volume (MPV) was higher in the HE group compared with HU and control groups [9.5 (Interquartile range, IQR: 8.7-10.1), 8.4 (IQR: 7.7-9.1), and 8.3 (IQR: 7.7-8.7) fl, each p<0.001, respectively). In linear regression analysis, systolic BP (beta = 0.18, 95% confidence intervals (CI): 0.002-0.015, p < 0.007) and diabetes mellitus (beta = 0.24, 95% CI: 0.28-0.95, p < 0.001) were independently associated with MPV levels. Our findings show that MPV can be elevated in patients with HE and HU. It can be independently associated with systolic BP and diabetes mellitus. These findings imply that platelet activation contribute to the pathogenesis of thrombotic complications in hypertensive crises.