A 59-year-old man was diagnosed with clinical stage D1 poorly differentiated prostatic adenocarcinoma (PAC). The patient was treated with total androgen blockade therapy. The tumor recurred 18 months later. Digital rectal examination revealed a large, stony-hard prostate. The serum PSA level was within normal limits. Pathological examination of the prostate revealed conventional adenocarcinoma with large numbers of neuroendocrine (NE) cells. The patient died 3 months after the diagnosis of PAC with NE differentiation, 22 months after the initial diagnosis of prostate cancer.