Hyperparathyroidism is generally caused by a benign tumor of a parathyroid gland, which is located in the anterior neck, adjacent to the thyroid gland. The symptoms develop slowly and are initially slight. They can fester for many years and ultimately can become very disabling if left untreated. The diagnosis is generally considered when a patient is discovered as having an elevated serum calcium level. Patients with elevated calcium levels have hypercalcemia. We estimate that 2% of the general population has hypercalcemia and that approximately 1/3 of this group may prove to have hyperparathyroidism. Even people with mild hypercalcemia may have an etiology associated with parathyroid tumors. Once discovered and treated with surgery, patients can experience prompt significant resolution in symptoms.