Papillary carcinoma of the thyroid with mucoepidermoid features. The significance and differential diagnoses of signet-ring cells found in the fine-needle aspirate of metastatic mucoepidermoid carcinoma from the thyroid are reported and discussed. The primary tumor occurred in a 35-year-old man, who had a history of neck irradiation during his childhood. Despite postoperative treatment with 60 Gy external radiation and 1,200 mCi 131I, the patient has at present--12 years after the initial operation--progressive disease with local recurrence in the neck as well as lung metastases. 