Background: Pulmonary arterial hypertension (PAH) is a chronic progressive disease characterized by persistent elevation of pulmonary artery pressure. Vasoconstriction, remodeling, and thrombosis cause increased pulmonary vascular resistance and pressure. Previous studies have demonstrated that platelet activation occurs in patients with PAH. Our aim was to assess the mean platelet volume (MPV), an indicator of platelet activation in patients with PAH. Patients and Method: The study group consisted of 22 patients with PAH. An age-, gender-, and body mass index-matched control group was composed of 25 healthy volunteers. All patients underwent physical examination, echocardiography, and diagnostic cardiac catheterization. We measured serum MPV values and platelet counts in patients with PAH and control participant. Results: MPV was significantly higher among the patients with PAH when compared with control group (8.68 +/- 0.87 vs 8.02 +/- 0.68 fl, respectively; P = .006). Conclusion: We have shown that MPV was elevated in patients with PAH.