Three types of involvement of the rectum and recto-sigmoid by carcinoma of the prostate are reviewed through an analysis of eight cases. A fourth type with subserosal metastatic implant of the proximal sigmoid may occasionally be encountered. The roentgenographic findings are not pathognomonic, but are characteristic of extrinsic involvement of the bowel wall. When clinical symptoms are predominantly related to the bowel, carcinoma of the prostate is usually advanced. All patients presented with bone metastases, uretero-hydronephorsis, lack of function of one kidney, or both bone metastases and urinary tract obstruction. Rectoscopy and biopsy are helpful. However, biopsy specimens often show non-diagnostic features in secondary malignancy. Correct diagnosis is important, since there is a difference in treatment of primary carcinoma and of secondary involvement of the rectum by prostatic carcinoma. A diagnostic challenge exists if the patient is evaluated by barium enema examination for primary bowel symptoms, in particular, large bowel obstruction. At this time intravenous pyelography and bone survey for metastases may not be available to suggest the correct diagnosis. More widespread use of barium enema examinations in the evaluation of advanced carcinoma of the prostate is suggested, since the type of rectal disease shown on barium enema study was not clinically suspected in five of eight patients. The prognosis is usually unfavorable because of advanced carcinoma. Survival often does not exceed several months to one year. However, one of our patients is still well after three years of hormonal therapy.