Among the most interesting manifestations of neoplasms is the production of functional peptides and hormones that may induce unique clinical syndromes. It has become obvious in the last decades that a wide range of endocrine tumors secrete hormones not normally associated with the tissue in which the neoplasm arises. The resultant syndromes, some of which resemble other endocrine entities, can be the first clinical manifestation of malignant disease or a harbinger of cancer recurrence. The development of these disorders does not necessarily correlate with cancer stage or unfavorable prognosis. Early recognition of paraneoplastic endocrine syndromes is clinically important as it might lead to the detection of underlying malignancy and might prevent delay in treatment. Because paraneoplastic endocrine syndromes often cause considerable morbidity and mortality, effective treatment can improve patient quality and length of life. The aim of this study was to review the most common and the most specific paraneoplastic syndromes associated with the presence of ectopic hormone production. We emphasize the importance of considering the ectopic hormone production in the differential diagnosis of various endocrine entities.