The surgical treatment of thyroid cancer in the cat involves excision of one or both thyroid glands while sparing at least one parathyroid gland. The most common postoperative complication of bilateral thyroidectomy is transient hypocalcemia. Most feline thyroid tumors are benign, hyperfunctional thyroid adenomas. Surgical excision is usually curative. Canine thyroid cancer is most commonly malignant and nonfunctional. Successful surgical treatment of canine thyroid cancer depends on histologic and early diagnosis prior to metastasis or invasion of the cancer into adjacent structures within the neck.