RESULTS: We enrolled 105 consecutive patients with COPD and PE; 29 patients of them (27.6%) with secondary polycythemia and 76 (72.4%) with no secondary polycythemia. Compared with those without polycythemia, the polycythemic group had significantly lower PaO2 and SpO2, as well as higher PaCO2 on arterial blood gas analyses (p<0.001, p<0.001 and p=0.002, respectively). More polycythemic patients were in the stage D Group (high symptoms and high risk) of the 2011 GOLD classification (51.72% vs. 26.32% in the non-polycythemic, p=0.014). They also had higher more severe pulmonary hypertension, and with greater frequency of centrally located or bilateral pulmonary thrombi. Multivariate logistic regression analysis revealed that sPO2, PASP, main pulmonary artery embolism and polycythemia were the risk factors associated with the PE mortality in COPD patients.