Introduction: Among patients with malignant solid tumors, 3-26% have pulmonary tumor embolism at autopsy. Symptomatic pulmonary micro-embolism is a rare, difficult to diagnose complication which may appear in a patient diagnosed with cancer or with occult neoplasia. In most cases the diagnosis is made postmortem. Methods: We want to present the cases of two patients known with cervical cancer and prostatic neoplasia, respectively, with advanced, metastatic disease, who came to hospital with signs and symptoms of acute respiratory failure and right heart failure. The patients were in critical condition with intense dyspnea, polypnea, central cyanosis, tachycardia; the ECG showed signs of right ventricular strain; the arterial blood gas analysis revealed respiratory alkalosis and hypoxemia; echocardiography showed enlarged right chambers, severe right ventricular systolic dysfunction, paradoxical motion of interventricular septum. One of the patients underwent thoracic computed tomography with contrast (the other patient had acute renal failure) which didn’t find any signs of pulmonary thromboembolism. Results: Because in both cases there was a high index of suspicion of pulmonary thromboembolism, the patients received unfractionated heparin. The evolution was unfavorable with the death of the patients shortly after hospital admission. At the autopsy it hadn’t been found macroscopic thrombotic material in the pulmonary artery. The microscopic examination of the pulmonary biopsies showed multiple occlusive tumor micro-emboli in the small pulmonary arteries. Conclusions: Pulmonary tumor micro-embolism must be considered in case of a clinical picture suggestive of pulmonary thromboembolism in a patient with cancer, when the CT scan is negative for pulmonary embolism and when there is no response at the anticoagulant therapy. The correct diagnose could help avoiding the administration of anticoagulant therapy or fi brinolysis. Although there is no specifi c therapy, it has been considered: surgical excision of the tumor, placement of inferior vena cava fi lter, chemotherapy