A male, 74 years old patient with perineal, sacral pain and with defecation disorders attended the outpatient clinic of HIETE. The origine of the complains was a retrorectal, fist like, rectum narrowing tumor. The tumor was covered by normal mucosa from rectal side. Preoperative examinations--endoscopy, CT, MRI transrectal US--detected a tumor with size 7 x 6 x 5 cm, growing from the muscular wall of the rectum, with no connection with the surrounding tissues. Deep biopsy revealed malignant mesenchymal tumor. After preoperative irradiation abdominoperineal rectum amputation was performed. The recovery was uneventful. The definitive hystological examination proved a gastrointestinal stromal tumor (GIST). This type of tumor rarely occurs in the large intestine or in the rectum, that why the publishing can be interesting.