AbstractMedullary carcinoma of the thyroid (MCT) is a rare tumor which, since its identification by Hazard et al. [2] in 1959, has attracted interest for 2 reasons. First, the secretion of the tumor marker, thyrocalcitonin, provides a means of making the diagnosis of MCT before the tumor is clinically evident. Second, MCT may be associated with pheochromocytoma and parathyroid hyperplasia as the autosomal dominant familial syndrome of multiple endocrine neoplasia, type II (MEN II). MCT may occur sporadically. When MCT is encountered in the familial form the natural history varies from family to family and also in individuals within a specific kindred. This variation creates difficulties in management and in reaching the decision for an aggressive approach to surgical treatment.