|Ectopic parathyroid gland is a major cause of persistent and recurrent hyperparathyroidism and the success of parathyroid surgery depends on the accurate preoperative localization of parathyroid adenoma. We report a case of 52-year-old male suffered from primary hyperparathyroidism for several years, caused by ectopic mediastinal parathyroid adenoma that was detected by 99mTc-sestamibi scan with single photon emission computed tomography(SPECT). Four years ago, he visited to Department of Urology because of ureter stone and performed extracorporeal shock-wave lithotripsy(ESWL). At that time, he had also complained vague symptoms of general weakness, headache, thirst and dyspepsia. The laboratory findings showed hypercalcemia(14.0 mg/dL, reference value; 8.2~10.8) and increased intact PTH level (246.7 pg/mL, reference value;14~72), suggesting primary hyperparathyroidism. We performed parathyroid scan and ultrasonography but failed to localize the lesion. With the medical treatment, his calcium level decreased to the 11.3 mg/dL. Patient revisited outpatient department complaining symptoms of headache, dyspepsia, and recurrent urinary symptoms, showing persistent primary hyperparathyroidism: hypercalcemia (15.5 mg/dL), hypercalciuria (311.5 mg/day) and increased intact PTH level (300.6 pg/mL). In addition, renal function was decreased and severe osteoporosis were found. Early and delayed 99mTc-MIBI scan were obtained at 15 minutes and 2 hours, but again failed to localized the lesion. We then carried out SPECT images after isotope injection, and found ectopic parathyroid uptake on upper anterior mediastinum (1.7×1.3×1.8 cm). The mass was excised by median sternotomy and diagnosed as parathyroid adenoma. After excision his general condition markedly improved, maintaining normocalcemia (8.5 mg/dl) with supplementation of 800 mg elementary calcium. In conclusion, 99mTc-MIBI scan followed by SPECT could permit better localization, especially for mediastinal adenoma in persistant or recurrent hyperparathyroidism.