Eleven patients, three males and eight females, developed brain metastases from well-differentiated thyroid carcinoma 1 to 20 years after their original diagnosis. Two had brain metastases only and nine had metastases to the lungs and bones as well. Most patients died within a year of diagnosis of brain metastases. We conclude that brain metastasis from thyroid carcinoma carries a poor prognosis and that newer modalities of therapy may be needed.