TRUE IDIOPATHIC HYPOPARATHYROIDISM (THP) is a relatively rare disease, as evidenced by the fact that only 58 acceptable cases had been reported in the literature up to 1960 (Bronsky, 1958; Bergstrand, 1958; Buchs, 1955, 1957; Axelrod, 1950; Naef, 1959; Soper, 1957; Symon, 1959). Familial occurrence of THP is so uncommon that this disease is not usually thought of as being hereditary. Cases of THP presenting with hypocalcemic convulsions during the neonatal period or at ages less than one year are particularly unusual. It is the purpose of this paper to present two cases of neonatal THP occurring in siblings, together with evidence suggesting that there may be more than one type of THP, and that one type is transmitted as a sex-linked recessive trait. The requirements for acceptance of a case as THP were first set forth by Drake (1939) for idiopathic hypoparathyroidism and subsequently were modified by Bronsky (1958) to exclude pseudohypoparathyroidism. The criteria are: 1) low serum calcium

2) high serum phosphorus 3) chronic tetanyor convulsions 4) absence of roentgenologic signs of rickets or osteomalacia 5) absence of renal insufficiency, steatorrhea, chronic diarrhea, and alkalosis 6) absence of physical characteristics of pseudohypoparathyroidism, such as brachydactyly, dwarfing, or subcutaneous calcium deposition. Excluded from the category of THP were cases showing failure to respond to parathormone by increased urinary phosphorus excretion, and cases with meager or questionable clinical findings having demonstrable parathyroid glands on biopsy or post-mortem examination. However, in cases with clearcut clinical findings it wasnot required for inclusion as THP that response to parathormone be tested, or that biopsy or post-mortem examination be made. Some cases which may well have been THP had to be excluded because the information given in the reports was insufficient to permit distinction between THP and pseudohypoparathyroidism.