Most of the thyroid cancer associated with hyperthyroidism is papillary thyroid cancer. Medullary thyroid cancer (MCT) with hyperthyroidism case is reported extremely rare. We report a 63-year-old female with a MCT discovered during following-up for Graves' disease. We also review the recent therapeutic guideline for Graves' disease and the management of the thyroid nodules based on the clinical evaluation of this case.