Carcinoma of the thyroglossal duct. A review of 39 instances of excision of a cyst of the thyroglossal duct performed at St. Paul Medical Center, Dallas, Texas, revealed two patients with carcinoma of the thyroglossal duct. A review of the English literature yielded 146 instances of this uncommon tumor. Eighty-four per cent were papillary adenocarcinoma of thyroid type and 5 per cent were squamous cell carcinoma. The patients were from six to 81 years old with a 2:1 female to male ratio. Metastatic disease to lymph nodes was noted in 11 per cent and invasion of overlying strap muscles was found in 4 per cent. Carcinoma of the thyroid gland occurred in 14 per cent. Preoperative diagnosis was rare. The Sistrunk procedure is recommended for initial surgical therapy with further surgical or adjuvant therapy dependent on associated clinical findings. Prognosis for carcinoma of the thyroglossal duct of thyroid type parallels that of carcinoma of the thyroid gland. 