Eleven patients who continued to have elevated calcitonin (CT) levels after thyroidectomy and central node dissection for medullary carcinoma of the thyroid gland (MCT) were subjected to additional surgery. Metastatic MCT was found in the excised tissue from each patient. Normalization of CT values was obtained in four patients who had a few microscopic, unilateral metastases. In these patients an average of 13 normal lymph nodes were excised at reoperation for each metastasis. The results of the reoperative series demonstrate that it is possible, with meticulous neck dissection, to normalize CT levels in patients with microscopic metastases from MCT. Metastases that can be seen or palpated are always associated with microscopic lymph node metastases. Removal of such microscopic metastases is probably the key to achieving normal postoperative CT levels.