A unique case of carcinosarcoma of the prostate detected in a 71-year-old man is presented. Pelvic exenteration was performed, and the resected prostatic mass was found to consist of two histologically distinct elements; adenocarcinoma and sarcoma with focal osteosarcomatous element. The patient is still alive with neither metastasis nor recurrence. This is the 42nd case of carcinosarcoma of the prostate to be reported in the literature.