We studied 65 patients with hypercalcemia who had beed performed 201T1/99mTc subtraction scan, 21 of them were confirmed as parathyroid tumor (19 adenoma, 2 carcinoma). The diagnostic sensitivity of 201T1/99mTc subtraction scan for detecting parathyroid mass was 90.5%, specificity was 97.6%, ultrasonography was 80.6%, 58.8%, respectively. The causes of two false negative cases were relatively small size (1.5*1*8cm) compared to remainig cases and poor thallium uptake due to cystic necrosis of parathyroid adenorna. The one false positive case was non-functioning thyroid nodule. 21T1/99mTc subtraetion scan was simple, effective diagnostic tool and superior to ultrasonography for evaluating the parathyroid mass with high sensitivity and specificity.