ABSTRACT
Intestinal involvement is observed in a significant portion of patients diagnosed with endometriosis. Involvement is often on the serosal surface of the sigmoid colon. Rarely, it takes place in the colonic mucosa and lymph nodes, causing lumen obstruction. Colonoscopic biopsies may be insufficient in the differential diagnosis of malignancy and diverticulitis. We report a case of a 41-year-old premenopausal female patient with endometriosis located in the ampulla recti causing complete intestinal obstruction. Although having a significant rectal mucosal mass, the diagnosis could not be made with tissue samples taken by endoscopy. During the examination, the patient developed ileus. With the preliminary diagnosis of rectal cancer, surgical intervention was applied with oncological principles, and its treatment was performed with opening a diverting ileostomy. Diagnosis of rectosigmoid endometriosis is difficult. In women of childbearing age, rectosigmoid endometriosis should be kept in mind in lower gastrointestinal tract obstructions.