Primary adenocarcinomas of the retrorectal (presacral) space are uncommon and usually arise from cystic lesions developing from remnants of the embryological postanal gut (tail gut cysts) containing mucous-secreting epithelium. A singular case of a patient who presented with a retrorectal mass is described. A 70-year-old previously healthy man had a four-month history of perianal pain during defecation. Preoperative colonoscopy showed external compression of the lower rectum with normal mucosa; pelvic computed tomography demonstrated a 5.5 x 4.5 cm(2) retrorectal oval mass, originating from the posterior lower rectal wall, containing cystic components and some small calcifications. The tumor, after complete resection via transanal approach, was shown to be a very rare case of primary adenocarcinoma of the presacral space. The patient had an uneventful postoperative course and he is free from disease 4 years after surgery. Clinicopathological features and surgical treatment of this unusual tumor are discussed.