Background: Systemic thromboembolism is a serious complication in patients with aortic stenosis (AS). Previous studies have demonstrated that platelet activation occurs in patients with AS. The aim of this study was to assess the mean platelet volume (MPV), an indicator of platelet activation in patients with AS. Patients and Methods: The study group consisted of 43 patients with AS. An age-, gender-, and body mass index-matched control group consisted of 35 healthy volunteers. All patients and control participants underwent echocardiographic examination. We measured the serum MPV values in patients and control participants. Results: Mean platelet volume was significantly higher among patients with AS when compared with the control group (8.7 +/- 1.0 vs 7.9 +/- 0.9 fL, respectively; P = .001). Conclusion: We have shown that MPV was significantly elevated in patients with AS compared to control participant.