VERY little exact information is available on the etiology of idiopathic hypoparathyroidism. Since there are normally four parathyroid glands, the question arises as to what phathologic influence could exert itself in all four areas. A priori the loss of some trophic hormone, the presence of some circulating toxin with a specific affinity for parathyroid tissue, or the predilection on the part of the parathyroid glands for some infection (cf. adrenal glands and tuberculosis) might produce atrophy or destruction of all four glands. The authors know of on y two cases of undoubted idiopathic hypoparathyroidism to come to autopsy. As recorded in a previous paper from this clinic (1), the post mortem of a boy who died with idiopathic hypoparathyroidism showed complete aplasia of the epithelial cells of all four parathyroid glands with replacement by fat cells but with retention of the capsules. Cantarow, Stewart and Morgan (2) were unable to find parathyroid tissue in a patient with idiopathic hypoparathyroidism who died.