NEONATAL TETANY, a well-known clinical entity, has rarely been shown to be secondary to maternal hyperparathyroidism. Recognition of this relationship is most important, as it may result in the early diagnosis of hyperparathyroidism in the mother and prevention of involvement in future siblings. Friderichsen,1,2in 1938, first described the association of neonatal tetany with maternal hyperparathyroidism. It is noteworthy that the infant described by him developed symptoms at five months of age, when cows' milk was substituted for human breast milk. Walton,3subsequently reported the occurrence of severe tetany in two premature siblings; their mother was found to have a parathyroid adenoma, which was surgically extirpated. Talbot and associates,4briefly described two neonates with tetany at two days of age, born to mothers with hyperparathyroidism. Van Arsdell, Jr.,5in 1955, also alluded to maternal hyperparathyroidism as a cause of neonatal tetany. He reported a woman with