There continues to be controversy about every aspect of management of differentiated thyroid carcinoma. In an age-based risk group previously described, low-risk patients made up 62% of cases and had a death rate of only 1%. Recent reports from the Mayo Clinic have expanded the concept of the low-risk group to include 86% of all cases with a 2% death rate by utilizing several anatomic and pathologic criteria of risk. We offer here another multifactorial system for the identification of low-risk patients who made up 89.4% of all patient seen between 1961 and 1980 and who have a death rate of only 1.8%. The resultant high-risk group constitutes 11% of cases but carries a 46% mortality rate. The risk-group definition is completely clinical and is based on age, presence of distant metastases, and the size and extent of primary cancer. It can be used confidently at the operating table to select conservative surgical procedures in patients with negligible risk of death. Through the succeeding decades analyzed, from 1941 to 1980, the effectiveness of this clinical categorization has increased substantially in separating patients at high and low risk, so that a mortality rate ratio of 26:1 now exists between high- and low-risk groups, respectively.