Multiple primary tumors (MPT) are a well-known phenomenon. Rapid advancements in diagnostics and therapeutics have contributed to a significant improvement in the survival rates of cancer patients, and also in an increase in the incidence of cases with multiple primary neoplasms, such as synchronous primary carcinomas of the rectum and prostate. We present a case history of a small number of male patients with synchronous primary carcinomas of the rectum and prostate. Two of the three cases were treated with lower anterior resection (LAR) and radical retropublic prostatectomy (RRP) during the same operation, and 1 case was treated with abdominoperineal resection (APR) and RRP during the same operation. No significant complications occurred during these operations. Our experience with these 3 cases of synchronous primary carcinomas of the rectum and prostate indicated that LAR or APR and RRP can safely be performed in a single operation.