At least ten members in four generations of a large family had familial benign hypercalcaemia (FBH) (familial hypocalciuric hypercalcaemia). Three members of the family had had parathyroid explorations (one on two occasions) before it was realised that they did not have primary hyperparathyroidism. FBH resembles hyperparathyroidism in that the plasma phosphate level is often in the low-normal range and in that parathyroid hormone is often detectable in the plasma. Urinary excretion of calcium is exceptionally low in FBH; indices reflecting tubular handling of calcium, such as calcium excretion per litre of glomerular filtrate, are better than 24 h urinary calcium in discriminating between FBH and primary hyperparathyroidism.. FBH may be more common than is generally appreciated; it is important that it should be recognised so that patients may be spared unnecessary surgery.