We report a case of simultaneous occurrence of medullary carcinoma and papillary carcinoma of the thyroid in the same thyroid gland. Immunoreactivity of calcitonin, carcinoembryonic antigen, neuron specific enolase and thyroglobulin made a sharp distinction between both neoplasms of the thyroid. It appears reasonable to consider that simultaneous occurrence of medullary carcinoma and papillary carcinoma of the thyroid in this case does not have embryological or genetical significance.