A 38-year-old woman died of hemorrhagic shock caused by idiopathic bleeding in the abdominal cavity. At autopsy, more than 5,000 mL hemoperitoneum was detected. There was no remarkable bleeding site except for a small tear in the surface of the spleen. Microscopic examination suggested that isolated splenic vein thrombosis induced coagulative necrosis of the spleen and subsequently caused splenic laceration. Whenever a case of hemoperitoneum is encountered, splenic rupture should be included in the differential diagnosis; it is imperative to manage such cases as promptly as possible.