"BACKGROUND: Between 80 to 85% of patients with hyperparathyroidsm have a solitary adenoma of the parathyroid glands and another 15% have a parathyroid hyperplasia. Preoperative localization of the parathyoid glands is generally accepted as warranted in patients who have failed an initial attempt at parathyroidectomy, ectopic locations and inexperienced surgeons. Different imaging techniques have been used for detection of abnormal parathyroid glands such as high resolution ultrasonography, computerized tomography, arteriography, venous sampling or magnetic resonance imaging and 201Tl/99mTc subtraction scintigraphy. But these methods have had varying rates of success, with low specificity and low sensitivity. Among the several different techniques available for parathyroid radionuclide imaging, the most common is the use of a dualradioisotope procedure combining of Tl with Tc. However, there are some controversies regarding the optimal technical aspects of this procedure, including the relative amount of injected dose of radiotracers, failed detection for small sized and deeper cervical located parathyroids, and not easy procedures. Recently, double phase Tc-sestamibi scintigraphy would be useful to solve these technical limitations, more convenient and have higher sensitivities. The purpose of this study was to compare the diagnostic accuracy of 99mTc-sestamibi with 201Tl/ 99mTc subtraction scintigraphy in the localization of hyperparathyroidism. METHODS: 9 patients with hyperparathyroidism underwent preoperative evaluation with double phase 99mTc-sestamibi scintigraphy and 201Tl/99mTc subtraction scintigraphy for attempted localization of abnormal parathyroid glands and surgical explorations. Imaging results were compared to surgical findings. RESULTS: Of 9 patients, 7 had a solitary parathyroid adenoma, 1 had a carcinoma and 1 had parathyroid hyperplasia. The 201Tl/99mTc subtraction scintigraphy preoperatively localized 8 of 9 patients(sensitivity: S9%) and 99mTc-sestamibi scintigraphy correctly localized all lesions for a sensitivity of 100%. In one case, 201Tl/99mTc subtraction scan show only a hot uptake at left upper parathyroid area, but 99mTc-sestamibi scan was shown the three site of hot uptake at left upper, both inferior parathyroid area. CONCLUSION: In patients with hyperparathyoridism, 99mTc-sestamibi scintigraphy may be used as the single imaging technique as it show a very high sensitivity and specificity in the preoperative localization of pathological parathyroid glands.