This is the case of a 39 year old female who underwent an urgent laparotomy because of gut obstruction. Intraoperative impression was rectosigmoid carcinoma with frozen pelvis and assessed to be unresectable. hence a transverse colostomy was done. Although subsequent endoscopic and CEA evaluations gave the impression of intestinal endometriosis, malignancy could not be ruled out. Patient was started on Danazol and when it became ineffective, surgical control was contemplated. CT scan of the abdomen was done to assess for possible presence of abdominal malignancy and with a negative report, patient underwent abdominal subtotal hysterectomy, bilateral salpingo-oophorectomy, segmental resection of the rectosigmoid and appendectomy. Transverse colostomy was closed later. The objective of this paper was to report a case of complete rectosigmoid obstruction secondary to endometriosis, in order to demonstrate the difficulty in establishing an accurate diagnosis and the propensity of colonic endometriosis to mimic colon cancer.