The aim of this study was to investigate the prognostic role of mean platelet volume (MPV) in patients with coronary artery ectasia (CAE). The baseline MPV values of 258 patients with CAE were screened. The mean time of follow-up was 49 +/- 21 months for major adverse cardiac events (MACEs) defined as the combination of cardiac death, nonfatal myocardial infarction (MI), rehospitalization due to cardiac disorders, and readmission due to chest pain. During follow-up period, 63 (24%) MACEs developed. There were 4 (2%) cardiovascular deaths, 0 nonfatal MI, 14 (5%) rehospitalization, and 45 (17%) readmission. Mean platelet volume values were significantly higher in patients with CAE with MACEs than in patients with CAE without MACEs (9.5 +/- 1.2 fL vs 8.9 +/- 1.1 fL, respectively, P = .002). The rate of MACE was higher in CAE patients with MPV of >9 fL than those with MVP of <= 9 fL (33% vs. 15%, P = .001). Mean platelet volume has a prognostic value for MACEs in patients with CAE.