The paper deals with a study of 42 cases of medullary carcinoma which accounts for 12.6% of all forms of thyroid cancer. The female-to-male ratio was 1.3:1, mean age - 45 years. Medullary carcinoma occurs sporadically in cases of familial endocrine syndrome. A case of Sipple's syndrome is reported. Medullar carcinoma is a hormonally-active tumor which produces calcitonin, the latter serving as a tumor marker for this carcinoma. Medullary carcinoma is characterized by bilateral involvement of the thyroid, which is more frequent in cases of familial disease, and a high rate of incidence of regional metastases (82.5%). Apart from clinical diagnostic means, the disease is chiefly identified cytologically and by calcitonin assays in blood plasma. It is mainly treated by surgery; 5- and 10-year survival rates are 87.2 and 80%, respectively.