Cushing's syndrome (CS) is characterized by the overproduction of cortisol that may result in significant morbidity and mortality if left untreated. CS is very rarely caused by ectopic adrenocorticotropic hormone production from several tumors, although pulmonary neuroendocrine tumors (pNETs) are the most common etiology. It is controversial whether such tumors are more clinically aggressive than other pNETs. We herein report an unusual case of severe ectopic CS caused by a small pulmonary carcinoid in the lung with massive neoplastic dissemination to the liver. We highlight and discuss the unusual clinical onset, with diagnostic and therapeutic criticism, of this rare entity.