A very rare case of carcinosarcoma of the prostate is reported. The patient was a 77-year-old man in whom both primary and metastatic tumors presented the pathology of carcinosarcoma of the prostate. The carcinosarcoma was resistant to anti-androgen therapy, and the patient showed low level of serum prostatic acid phosphatase and was free from bony metastases despite multiple metastases to the lung, liver, pancreas, para-aortic lymph nodes, spleen and penis. The sarcomatous component consisted of chondrosarcoma and fibrosarcoma, both of which were positive for vimentin. The carcinomatous component was positive for both keratin and prostatic acid phosphatase.