Fifty-two cases of primary hyperparathyroidism were experienced at Kyoto University Hospital and affiliated hospitals between 1965 and 1990. Thirty-three of them (63%) were of the stone type, twelve (23%) of the bone or mixed type, seven (13%) of the chemical type. Histopathological findings showed adenoma in 49 cases and hyperplasia in 3 cases. Serum calcium levels decreased postoperatively in all cases of adenoma but unchanged in 2 of 3 cases of hyperplasia. For parathyroid adenoma, the accuracy of localization was more than 90% by the combination of computed tomography, magnetic resonance imaging, ultrasonography, subtraction scintigraphy with 201TI and 123I, venous sampling for parathyroid hormone and/or angiography. Simple removal of parathyroid adenoma may be recommended in a case of primary hyperparathyroidism due to a single adenoma which was revealed by preoperative image diagnosis.