Ectopic mediastinal parathyroid adenomas are rare, but can be life-threatening. Resection is indicated in those cases accompanied by hypercalcemia, especially in young patients. Although most mediastinal parathyroid adenomas can be removed by a cervical approach, a transthoracic approach is needed when the adenoid tissues are located deep within the thoracic cavity. We describe the case of a 37-year-old female who underwent excision of an intrathoracic ectopic parathyroid adenoma after parathyroidectomy four months earlier.