A 13-year-old 4.6-kg (10.2-lb) neutered male domestic long hair cat was evaluated because of a history of lethargy, exercise intolerance, and ventroflexion of the cervical portion of the vertebral column. After extensive assessment at the Veterinary Teaching Hospital at Michigan State University, the clinical signs were attributed to an aldosterone-secreting tumor of the adrenal gland. Subsequently, an insulin-secreting tumor of the pancreas as well as a functional parathyroid gland adenoma were diagnosed. All 3 masses were surgically removed, and the cat made a full recovery with complete resolution of clinical signs. The syndrome of multiple endocrine neoplasia is well described in humans, and the heritability of the condition has been confirmed. In cats and other species with 1 or more endocrine neoplasms, it is important to perform thorough clinical assessments of patients to identify other endocrine organs that may also be affected concurrently with neoplastic disease.