We analyzed patients diagnosed premortem with pulmonary thromboembolism (PTE), focusing on causes of failure of therapy together with clinical characteristics. Methods: This was a retrospective study of 25 cases. We classified PTE as massive, submassive and nonmassive. Results: Of the 25 cases, 76% (19/25) had two or more risk factors for PTE. The point of origin of PE could be determined in only 44% of 25 cases. In 20 % (5/25) of cases diagnosed with PTE a maximum 3 months prior to death, the main cause of death was unknown. Of 10/20 (50%) massive and 8/20 (40%) submassive PTE cases, 5 and 3 underwent thrombolysis therapy, respectively. Both of 2/20 (10%) non-massive PTE cases underwent LMWH; in 1 of these cases, autopsy showed thrombus of a large pulmonary artery at 25 days after therapy. Submassive PTE cases were older and had a greater number of risk factors than did massive PTE cases. The point of origin of PTE was a right heart thrombus in six (24%) cases. Surgeries were performed in 3/6 (50%) cases with right atrial thrombus. The survival duration after therapy in those who underwent surgery was longer than those who received thrombolysis and LMWH therapies. Conclusion: Physicians may provide appropriate information to patients who have certain risk factors (trauma, surgery, pregnancy, etc.) to predict acute PE at a preventable stage. If risk factors are present, or if new risk factors for PTE are identified, patients should be followed up carefully due to the risk of thrombosis progression.