Ectopic adrenocorticotropin (ACTH) secretion accounts for less than 10% of all causes of endogenous Cushing's syndrome (CS) and is usually associated with neuroendocrine tumors and small cell carcinoma of the lung. We report the case of a 62-year-old man with CS due to ectopic ACTH production by small cell carcinoma of the prostate. He presented with severe hypercortisolism and associated symptoms. Plasma neuron specific enolase (NSE) was grossly elevated. Despite performing a laparoscopic bilateral adrenalectomy, the patient died as a result of sepsis with multi-organ failure. Post-mortem immunohistochemical staining of prostate tumor tissue showed ACTH expression. ACTH staining was also performed in four additional patients with small cell carcinoma of the urinary tract without CS. None of these additional cases showed a positive staining for ACTH. Although a rare cause of ectopic ACTH production, neuroendocrine prostate carcinoma should be considered in male patients with Cushing's syndrome, in particular in those with an occult source of ACTH overproduction.