From the *Department of Pediatrics, and the †Department of Medical Genetics, Doernbecher Memorial Hospital for Children,

and accepted October 1989. Familial hypocalciuric hypercalcemia (FHH) is a benign autosomal dominant disorder. In-fants affected with FHH however, born to unaffected mothers may develop life-threatening autonomous hyperparathyroidism, the mechanism of which is not clearly understood. There is little information recorded in the literature regarding the opposite scenario, i.e., unaffected infants born to affected mothers. Because fetal parathyroid suppression presumably occurs secondary to high maternal calciums, neonatal hypocalcemia would be expected. The authors present a case of an infant with the latter circumstances who presents with late onset, life-threat-ening hypocalcemia secondary to relative hypoparathyroidism. The authors explored the possi-bility that vitamin D deficiency and/or acute environmental stress facilitated the decompensa-tion. The patient required therapy for 2 months. FAMILIAL HYPOCALCIURIC HYPERCAL-AMILIAL HYPOCALCIURIC H CEMIA (FHH) is an autosomal dominant disorder in which renal reabsorption of filtered calcium and magnesium is enhanced. Affected individuals hav