Although rectal procidentia is not an uncommon disease, presentation of more proximal segments of the large bowel through the anus is extremely rare. A case with sigmoido-recto-anal prolapse secondary to a large adenoma of the sigmoid colon is reported herein. A 28-yr-old man with an anal prolapsing mass was admitted to our hospital. Preoperative CT scan showed a sigmoid-recto-anal prolapse. An emergency operation was decided upon because the prolapsed segment was irreducible and because its viability was questionable. After a manual reduction of the mass, an anterior resection was performed under general anesthesia. The pathologic diagnosis of the resected specimen was a large villo-tubular adenoma.