Endocrine tumors constitute a large group of neoplasms that are widely dispersed throughout the body. They are made up mostly of neuroendocrine tumors (NE), which are characterized by the presence of secretory granules and production of peptide hormones, and non-NE tumors such as those derived from thyroid follicular cells and adrenal cortical cells. Immunohistochemical markers have been used to characterize these lesions and distinguish them from other histologically similar tumors. Chromogranin and synaptophysin are the most widely used broad-spectrum neuroendocrine tumor markers. The use of antibodies to transcription factors, keratins, and specific peptides is quite valuable in the diagnosis of endocrine tumors. This article reviews the common markers used to characterize endocrine tumors and to recognize tumors involved in the differential diagnosis of specific lesions.