PURPOSE: To evaluate the radiologic findings and detectability of parathyroid masses in ultrasonograph computed tomography(CT), and radionuclide study(201TI-99mTc pertechnetate subtraction scintigraphy). MATERIALS AND METHODS: Surgically-proven 11 cases with parathyroid masses consisted of adenoma(n=8), adenomatous hyperplasia(n:2) and adenocarcinoma(n:l) were retrospectively analyzed. We performed US in all cases, CT in 8 cases, and radionuclide study in 7 cases. The parathyroid masses were analysed in regard to anatomic localization and imaging appearance on three modalities. RESULTS: Ten of the 11 parathyroid masses(91%) were located posterior to the thyroid gland and the remainder in the left superior mediastinum. Nine of the 11 cases(82%) were detected on US. The majority were well-defined hypoechoic mass on US. Six of the 8 cases(75%) were detected on CT scan. In the precontrst CT, all of the 8 masses were hypodense as compared with thyroid gland and most showed mild enhancement on post-contrast CT. Six of the 7 cases(86%) were detected on RI study as hot nodule. CONCLUSION: The typical radiological findings of the parathyroid mass were well-defined ovoid or round hypoechoic mass on US, hypodense mass with variable contrast enhancement on CT, and hot nodule on radionuclide study. US was a convenient and reliable imaging modality in detecting parathyroid masses. Improved diagnostic accuracy could be achieved with complementary CT scan and radionuclide study in addition to ultrasonography.