In October 14, 1982, a 30-year-old male was admitted to the hospital because of a left flank pain and melena. On undergoing testing, an upper gastrointestinal series revealed barium retention in the small bowel, in which an abdomen X-p showed an abnormal gas shadow. Endoscopic examinations revealed depressive lesions, and the histological diagnosis was malignant neoplasm with a duodenal wall infiltration. A superior mesentric arteriogram showed the dilatation of the media colic artery and neovascular lesions. Thus a leiomyosarcoma of the small intestine was suspected, and the patient underwent surgery on November 15. The tumor was sack-like and looked black; histologically it was diagnosed as a small intestine, because the primary origin was only detected in the small intestine. Four months after the operation, the tumor recurred and the patient died in June, 1983.