Thyroidectomy has become a fairly common surgical procedure in small animals because of the increasing incidence of thyroid tumors. Surgical removal of the thyroid gland can be routine or quite challenging, depending on the species (cat vs. dog) and the size and aggressiveness of the tumor. Many problems may be encountered with these patients, associated both with the disease and with the surgical treatment. Both thyroid and parathyroid tumors result in many alterations in the animal’s homeostasis. These alterations must be recognized by the surgeon to maximize the chance of a successful outcome. This chapter deals with thyroidectomy and parathyroidectomy in dogs and cats. Indications for surgery, pathophysiology of thyroid and parathyroid neoplasia, preoperative care, surgical procedures, and postoperative care and complications will be discussed.