Identification of RET gene mutations in patients at-risk for the development of the hereditary forms of medullary thyroid carcinoma has simplified management and expanded the scope of indications for surgical intervention. Patients who carry this mutation can be offered thyroidectomy at a very young age, hopefully at a point when the cancer has not yet developed or spread. Those who are found not to have inherited the mutation are spared further genetic and biochemical screening. This achievement marks a new paradigm in surgery--the recommendation that an operation be performed based on the result of a genetic test. Experience with management of patients with multiple endocrine neoplasia types 2A and 2B and with familial, non-multiple endocrine neoplasia medullary thyroid carcinoma will provide information that will aid in the future management of patients with other hereditary cancers.