A 61-year-old man diagnosed with poorly differentiated adenocarcinoma of the prostate (T4 NxM0, stage C) underwent endocrine therapy. The reduction of the tumor was recognized but soon annular rectal stricture appeared. In spite of the subsequent chemotherapy, symptoms aggravated. Then total pelvic exenteration and colostomy were performed. Prostate was easily separated from the rectal wall and the tumor continuity was not proved. Immunohistochemical inspection indicated that the origin of the tumor cells of the rectum was the prostate. Histopathological examination of the rectum using the step section method showed no trace of cancer invasion but many cancer cells in the intramural lymphatic duct. We concluded that adenocarcinoma of the prostate metastasized to the rectum by way of lymphatic flow and caused the annular stricture of the rectum.