The most important long-term complication of pulmonary thromboembolism is chronic thromboembolic pulmonary hypertension (CTEPH) that is associated with considerable morbidity and mortality. It is uncertain why some patients with acute pulmonary embolism (PE) develop CTEPH and others do not. Elevated red cell distribution width (RDW) has been associated with adverse outcomes of heart failure, PE, and idiopathic pulmonary hypertension. The aim of the present study was to investigate whether RDW might be a predictor of CTEPH in PE patients or not. This study is a retrospective cohort study. A total of 203 consecutive patients with acute PE were included. The RDW was higher in the CTEPH patients than the patients without CTEPH (17.04 +/- 3.46, 14.64 +/- 1.82, respectively, p = 0.015). RDW was also higher in the CTEPH patients at the time of diagnosis of CTEPH during follow-up compared with the baseline RDW level at the time of PE diagnosis (18.63 +/- 3.58, 17.02 +/- 3.59, respectively, p = 0.014). The optimal cutoff value of the RDW for predicting CTEPH was 14.65. The area under the curve of RDW for the prediction of CTEPH was 0.735 (95% confidence interval (CI): 0.600-0.869); in cases with RDW levels >14.65%, the specificity, sensitivity, and negative predictive value for CTEPH were 62% (95% CI: 0.55-0.69), 75% (95% CI: 0.47-0.92), and 96.7% (95% CI: 0.91-0.99), respectively. A multivariate regression analysis showed that RDW, hazard ratio: 1.58 (95% CI: 1.09-2.30), was a predictor of CTEPH (p = 0.016). High level of RDW was an independent predictor of CTEPH in PE patients. Therefore, RDW levels may provide a prediction for CTEPH in PE patients.