Frequent studies of the survival rates of patients with malignant disease of the thyroid are necessary to evaluate the results of treatment. We realize that even a 10-year follow-up of patients with low-grade malignancy of the thyroid is insufficient to provide accurate information with respect to cure rates, for, with or without treatment, a significant number of these patients will survive more than 10 years. However, a 10-year follow-up study of those patients with the more malignant neoplasms of the thyroid does provide a fairly accurate picture of the ultimate cure rate. Accordingly, we have conducted a long-term study of survival rates in our patients with malignancy of the thyroid, treated at the Illinois Research and Educational Hospitals during the period from January, 1936, to May, 1959. Source and Incidence of Patients with Malignant Thyroid Disease From January, 1936, until May, 1959, we have seen 128 patients with malignant disease