We describe a 47-year-old woman with a 13-year history of asymptomatic midline submental swelling. Cytologic examination of a fine-needle aspiration specimen from the solid mass revealed adenocarcinoma. The preoperative diagnosis was thyroglossal duct carcinoma. A Sistrunk procedure was performed and microscopic examination revealed papillary adenocarcinoma. The postoperative course was uneventful and there were no signs of local recurrence or metastasis at one year after surgery.