Septic pulmonary embolism (SPE) is an uncommon disease in which a microorganism- containing thrombus causes an inflammatory reaction and a mechanical obstruction in the vascular system of the lungs. Usually it is associated with tricuspid valve vegetation, septic thrombophlebitis or infected venous catheters. We present a rare and fatal case of massive septic pulmonary thromboembolism occurred in a diabetic woman, who complained in previous days dyspnoea, abdominal pain and nausea. Autopsy findings showed evidence of an erosive cystitis, while lungs examination showed total occlusion of pulmonary circulation system due to thrombo-embolic clots. In literature cases report about an association between septic pulmonary thromboembolism and erosive cystitis haven't been reported. So, we here show the first reported fatal case of a septic pulmonary thromboembolism as a lethal evolution of an erosive cystitis.