Hypoparathyroidism: Underfunction of the parathyroid glands with deficient production of the hormone parathormone which leads to low blood calcium (hypocalcemia). The parathyroid glands are located adjacent to the thyroid gland. They may be missing due to a birth defect, impaired by autoimmune disease, or surgically removed during thyroid surgery. Treatment is with oral calcium supplements and oral vitamin D. Oral vitamin D increases the gut absorption of calcium in the diet and helps to maintain normal blood calcium levels.