Ultrasonography was used preoperatively on nine patients with primary hyperparathyroidism in an effort to localize lesions in the parathroid glands. The causes of primary hyperparathyroidism were seven adenomas, one parathyroid cyst and one chief cell hyperplasia. Ultrasonography detected solitary mass in seven patients. In the remaining two patients, ultrasonography failed to discover such mass. We concluded that ultrasonography is valuable in the preoperative assessment of primary hyperparathyroidism as initial study of choice for localizing tumors.