We experienced a case of multiple endocrine neoplasia type 2A(MEN2A)diagnosed with medullary thyroid carcinoma. The patient was a 50s woman who was referred for a thyroid nodule detected in the right lobe during a carotid ultrasound examination. After undergoing a hemithyroidectomy, it was determined that the tumor was medullary carcinoma. RET gene test was performed, confirming a mutation at codon768, leading to the diagnosis of MEN2A. A completion thyroidectomy was performed to remove the remaining thyroid tissue. Postoperatively, the patient is undergoing systemic surveillance.