A kindred is described, six members of which fulfilled criteria for the syndrome of familial hypocalciuric hypercalcaemia (FHH). The majority of these individuals were asymptomatic: their hypercalcaemia was revealed by biochemical screening after parathyroid surgery had failed to diminish the elevated serum calcium concentration of the index case. In contrast to those members of the family diagnosed as adults, the daughter subsequently born to the index case included in her expression of FHH clinical features of severe neonatal primary hyperparathyroidism. Four hyperplastic parathyroid glands were excised, and following surgical intervention the baby improved clinically and accelerated the healing of her skeletal lesions. Her case suggests that an association does exist between FHH and neonatal primary hyperparathyroidism. Of the ten individuals at risk, inheritance of hypocalciuric hypercalcaemia was paralleled in eight cases by inheritance of the HLA haplotype All BW55 CW3 DR4. Such possible linkage has not previously been reported.