A 53-year-old female was suddenly hospitalized with acute left lateral abdominal pain. There was no history of trauma to the abdomen. She had received no abdominal operation. X-ray showed a soft tissue shadow in the left flank which displaced the bowel shadows medially. Plain abdominal CT showed a left retroperitoneal hematoma. Dynamic abdominal CT showed an outflow of medium from a blood vessel in the hematoma. At laparotomy, the source of bleeding was found to be the left ovarian artery. The ovarian artery was dilated and meandered remarkably. The ovarian artery and vein were ligated proximally and left adenectomy was performed. The patient made an uneventful recovery. Histological examination suggested a spontaneous rupture of a dissection of the left ovarian artery.