A 35 year old woman with hypercalcitoninemia was scheduled for an operation to treat her medullary thyroid cancer (MTC). TIVA with propofol and remifentanil was planned, and about 3 minutes after the infusion of anesthetics, her heart rate was suddenly elevated to 180/min and the systolic blood pressure was lowered to nearly 50 mmHg. The blood pressure returned to normal after the injection of phenylephrine 100 µg and a rapid infusion of 700 ml crystalloid solution. After the operation, bilateral pheochromocytoma and a RET proto-oncogene mutation related with multiple endocrine neoplasia 2A (MEN-2A) were found. Patients with MTC can present with peripheral vasodilation and relative hypovolemia that are related with hypercalcitoninemia. Patients with MEN-2A can be anesthetized for a MTC operation without the appropriate preparation for their pheochromocytoma. Therefore, we suggest that patients with MTC and hypercalcitoninemia should be cautiously anesthetized with TIVA. They also should be screened for pheochromocytoma and the RET proto-oncogene mutation to prevent deleterious hemodynamic events during anesthesia.