Carbon monoxide (CO) poisoning is frequent and can lead to high morbidity and mortality. Some studies have indicated increased platelet activation and aggregation in CO poisoning. Thus, we investigated mean platelet volume (MPV), an indicator of platelet activation, in patients with CO poisoning. We included 193 (117 women) patients who presented with a diagnosis of CO poisoning between June 2011 and March 2013. Control group was composed of 39 (15 women) patients. Troponin and creatine kinase MB levels were significantly higher in the CO poisoning group. Platelet counts were significantly higher in patients with CO poisoning (281 +/- 76 vs 248 +/- 65 x 10(9), respectively; P = .01). Similarly, MPV was significantly higher in the CO poisoning group (8.9 +/- 0.8 vs 7.9 +/- 0.9 fL, respectively; P < .001). Elevated MPV values may indicate that patients with CO poisoning have a higher risk of thromboembolic and cardiovascular complications due to platelet activation.