Primary hyperparathyroidism may be cured by removing the adenoma or overactive parathyroid glands. Primary hyperparathyroidism is usually caused by a tumor within the parathyroid gland. In 1961 Sipple described a combination of a pheochromocytoma, medullary thyroid carcinoma and parathyroid adenoma. Primary hyperparathyroidism results from a hyperfunction of the parathyroid glands themselves. Symptoms depend on whether the hyperparathyroidism is the result of parathyroid overactivity or secondary. Hypoparathyroidism is decreased function of the parathyroid glands with underproduction of parathyroid hormone. The normal glands respond by secreting parathyroid hormone at a persistently high rate. This is dependent on several histologic features within the abnormal parathyroid gland itself. Many conditions are associated with disorders of the function of the parathyroid gland. The osteoclasts do not have receptors for parathyroid hormone (PTH). PTH is secreted primarily by the chief cells of the parathyroid glands. Hypoparathyroidism will occur after surgical removal of the parathyroid glands. Calcimimetics reduce the amount of parathyroid hormone released by the parathyroid glands. Surgical removal of a parathyroid tumor eliminates the symptoms in most patients. Surgery is the only cure for parathyroid adenomas.