A 60-year-old man noticed rapid enlargement of a long-standing thyroid goitre, with dysphagia and difficulty in breathing. Thyrotoxicosis was diagnosed. Chest X-ray revealed multiple pulmonary metastases. He underwent near-total thyroidectomy. The histopathology revealed an undifferentiated thyroid carcinoma with some areas of papillary carcinoma and its follicular variant. Postoperative 131I total body scan showed residual thyroid tissue in the neck and one functioning metastasis in the right rib, posteriorly. The patient's condition deteriorated rapidly and he died from pneumonia. The autopsy showed widespread metastases of undifferentiated thyroid carcinoma. Only the right rib contained the follicular variant of papillary carcinoma.