Follow-up examinations were performed on 76% of 200 thyroid carcinoma patients treated at the University of Michigan Hospital over a 14-yr period. Twenty-two per cent of the patients died and 2% were lost to follow-up. In 82 patients, concentration of I131was demonstrable in metastases. In 52 of the 82, the metastases were to regional lymph nodes, and 35 of the 52 were apparently free of their thyroid carcinoma. In 30 of the 82, the metastases were to distant structures (lungs, bones), and 16 of the 30 showed complete clinical regression. Those patients who died of carcinoma did so within an average period of 2 yr after treatment, and no patient clinically free for 3 yr after completing treatment has had a recurrence to this date.