The results of several pre-operative localizing methods and pathological findings were compared in 11 patients with primary hyperparathyroidism. 1. The accuracy rate was highest with selective blood sampling from the thyroid vein and MRI, which was 75% with both methods. The 3rd was dual photon scintigraphy, the accuracy rate being 62.5%. The 4th was ultrasonography, 57.1%, and the rate was lowest with CT, 25%. 2. MRI-a new localizing method-has a weak point that it cannot differentiate lymph nodes from parathyroid adenoma/hyperplasia. 3. Not to overlook small lesion of primary hyperplasia, several localizing methods should be performed before initial neck exploration.