Hyperparathyroidism is a condition where the parathyroid glands, located in the neck near the thyroid gland, make too much parathyroid hormone. The excess amounts of parathyroid hormone act on the kidney, bones, and vitamin D metabolism to raise blood calcium levels.

Patients often get osteoporosis, kidney stones, and a number of different symptoms of the high calcium including fatigue, weakness, excessive urination, dehydration, depression, and abdominal pain.

A small proportion of patients with pituitary tumors have an inherited defect in a gene that can also cause hyperparathyroidism. This condition is called MEN-1.

Patients may also get pancreatic tumors that produce insulin or gastrin.