Background and Objectives: Medullary thyroid carcinoma(MTC) is a rare tumor derived from the parafollicular C cells of the thyroid gland accounting for 5-10% of all thyroid malignancies. In Korea, there has been a few case report of medullary thyroid carcinoma(MTC) but their clinical analysis were not exactly studied. So, we made clinical study of 10 patients diagnosed as medullary thyroid carcinoma. Materials and Methods: We reviewed clinical data of 10 patients who were diagnosed as medullary thyroid carcinoma(MTC) from April 1973 to August 1998 at National Medical Center. Results: The incidence of MTC was 2.3% of all thyroid cancer and their mean age were 44.2 years old. Preoperative thyroid scan showed cold nodule in all patients and thyroid function test(TFT) was within normal range. Of the 10 patents, only 4 patients had diagnosis of MTC in preoperative fine needle aspiration biopsy. All the patients underwent total thyroidectomy with central neck dissection. Two patients with cervical lymph node metastasis underwent total thyroidectomy, central neck dissection and modified neck dissection. Two patients (20%) showed recurrence at the site of neck, lung, mediastinum, bone and liver. Conclusion: Most MTC is sporadic form and have peak incidence in the fifth decade and female preponderance. Preoperative fine needle aspiration biopsy is considered to be a clinically useful diagnostic method, but its accuracy is not considered as much high as others. Total thyroidectomy with central neck dissection may be an useful surgical modality in treating medullary thyroid carcinoma.