The origin of medullary thyroid carcinoma and papillary thyroid carcinoma are embryogenically different, so these tumors have been thought to be independent of each other. We experienced a case of concurrent medullary and papillary thyroid carcinoma in one patient. The patient underwent total thyroidectomy and both two tumors were located at different lobes, respectively. Both tumors showed their own characteristic pathologic and immunohistochemical findings. The patient's elevated calcitonin level returned to the normal range after operation and there has been no evidence of recurrence. It is still controversial whether the concurrency is just coincidental or it arises from activation of a common tumorigenic pathway.