Mean platelet volume (MPV), a determinant of platelet function, is a newly emerging risk factor for atherothrombosis. The present study was designed to evaluate MPV in patients with obesity compared with non-obese control subjects. We selected 100 non-obese subjects and 100 subjects with obesity [body mass index (BMI) ≥30 kg/m2] matched for age and gender. The MPV was significantly higher in obese group than in non-obese control group (10.3 ± 1.2 vs. 9.0 ± 0.8 fl, p < 0.01). MPV was positively correlated with BMI in obese group (p < 0.05). Increased MPV may be a possible cause for increased cardiovascular risk in patients with obesity.