Parathyroid adenomas are the most frequent cause of primary hyperparathyroidism. In this article, we report a 44-year-old male patient with fatigue, hypercalcemia and hyperparathyroidism. Parathyroid scintigraphy and thoracic computed tomography revealed a lesion consistent with parathyroid adenoma ectopically located in the anterior mediastinum. The parathyroid adenoma was excised successfully under the guidance of intraoperative gamma probe. It is essential to determine the localization of parathyroid adenomas preoperatively. Therefore; ultrasonography, parathyroid scintigraphy and guidance of intraoperative gamma probe in patients with positive parathyroid scintigraphy are crucial for diagnosis and success of surgical treatment.