Approximately 100,000 new cases of primary hyperparathyroidism are diagnosed in the United States each year. Thus a disorder that was once considered to be rare is now known to be relatively common. Many patients with primary hyperparathyroidism are diagnosed today with only minimal hypercalcemia (serum calcium less than 1mg/dl above the upper limit of normal) and many have few or no classic symptoms or clinical manifestations of hyperparathyroidism, such as kidney stones or osteitis fibrosa cystica. Many patients with hyperparathyroidism today have fatigue or increased lethargy, muscular weakness, bone or joint pain and depression. It is difficult preoperatively to know whether these clinical manifestations are related to the primary hyperparathyroidism or not. Our own studies suggest that in about 80 per cent of patients with hyperparathyroidism the preoperative symptoms either improve or disappear after parathyroidectomy.