Because of the diverse nature of endocrine organs, and their vast range of physiologic functions, endocrine tumors encompass a wide range of origination sites and disease entities. The clinical picture of affected individuals is highly dependent on the tissue of origin, and the presence or absence of functional hormone secretions. Identification, localization, and therapeutic strategies, as well as prognosis can vary greatly. Many endocrine tumors have been described in human as well as veterinary patients. This article focuses on endocrine tumors of dogs and cats. Various tumors affecting the pancreas, thyroid, parathyroid, adrenal and pituitary glands are described, including insulinoma, gastrinoma, glucagonoma, and thyroid carcinoma, as well as parathyroid hormone- and growth hormone-secreting tumors. The syndrome of multiple endocrine neoplasia is also described.