We reviewed 27 patients who received preoperative localization using both parathyroid ultrasonography and parathyroid 201Tl-99mTc subtraction (TTS) scan from March 1986 to July 1993 in Chang Gung Memorial Hospital, Linkou. These 27 patients were diagnosed hyperparathyroidism by the pathological reports. There were 16 patients with primary hyperparathyroidism [PHPT; 9 males, 7 females; (mean age: 56.3 +/- 4.6 yrs)] and 11 patients with secondary hyperparathyroidism [SHPT; 8 males, 3 females; (mean age: 38.3 +/- 2.5 yrs)] due to end stage renal disease. The diagnostic accuracy was compared, and the results were as follow: (1) in localization of PHPT, the sensitivity and specificity of ultrasonography were 75.0% and 95.8% respectively, whereas the sensitivity and specificity of TTS were 87.5% and 100.0% respectively. The differences were not statistically significant; (2) the sensitivity and specificity of ultrasonography and TTS for patients with SHPT were 32.4% and 85.7% vs. 32.4% and 100.0%; and (3) higher sensitivity and specificity were achieved when both methods were chosen for localizing either PHPT or SHPT.