Background. The concept of NE differentiation in prostate carcinoma has two major aspects: prostate tumors with primary NE differentiation and NE differentiation occurred during hormonal therapy for prostate adenocarcinoma, with the extreme case of tumor dedifferentiation into a NE hormone resistant carcinoma.Material and method. The patient, 62 years old, with a history of poorly differentiated prostate adenocarcinoma, hormonally treated with the decrease and then constant maintenance of serum PSA level to 0.01 ng/mL was admitted in the hospital, 8 years after prostate tumor diagnosis, and 3 years after ceasing of hormone therapy, with multiple bone and liver metastases of unknown primary source.Results. The serum levels of CgA, NSE, CEA, CA19.9, serotonin were elevated. The histopathological examination of the needle biopsy fragment from a liver metastatic lesion revealed small cell neuroendocrine carcinoma. Despite the prompt chemotherapy, the disease has progressed, with the occurrence of brain metastases and the patient's death 6 months after detection of the metastatic disease.Conclusions. The present case confirms the diagnostic difficulties in llymetastatic undifferentiated small cells tumors, and on the other hand, draws attention to the possibility of NE dedifferentiation as a result of hormone deprivation in patients with prostate cancer.