Pulmonary tumor embolisms (PTE) are an infrequent cause of dyspnea in oncological patients. The majority are diagnosed in patients with advanced tumors, above all localized in the breast, lung or stomach. There are few published cases involving patients with urothelial tumors. We present the case of a 69 year-old male, without a previous diagnosis of cancer, who was admitted due to subacute dyspnea, with clinical suspicion of pulmonary thromboembolism (PT). The patient died on the fifth day of admission. The autopsy confirmed the existence of a tumor in the left renal pelvis with hepatic and lymphoganglionary metastasis and an extensive microvascular pulmonary embolism that affected a large part of the capillaries and medium-caliber blood vessels of both lungs. PTE were considered responsible for the progressive respiratory failure and as the final cause of death. The most frequent clinical presentation of PTE is dyspnea. They are often mistaken for PT and diagnosis is not easy. Their prognosis is very bad, with extremely high mortality and confirmation is usually post-mortem.