Background: Neuroendocrine cancer of the prostate can present in diverse clinical pictures, potentially hampering the diagnosis and probably leading to underdiagnosis. Methods: Two cases are presented corresponding respectively to two forms of the disease: de novo neuroendocrine cancer and dedifferenciation of an adenocarcinoma of the prostate to neuroendocrine cancer under long term luteinising hormone releasing hormone (LHRH) agonist treatment. Results: Suspicion of neuroendocrine cancer may be raised in prostate cancer patients presenting either clinical or radiological metastatic progression without prostate specific antigen (PSA) rise, or relatively extended metastatic disease right at diagnosis associated to relatively low PSA, yet any non-pulmonary visceral metastases. Neuroendocrine cancer of the prostate can also turn out to be the origin of an adenocarcinoma of unknown primary. Conclusion: In case these considerations are respected the risk of missing the correct diagnosis of a neuroendocrine cancer of the prostate may be minimised.