Eighty-four patients with recurrent kidney stones, serum calcium levels in the upper normal quartile, and most of whom with hypercalciuria had their parathyroids surgically explored. Parathyroid adenomata were found in 19 patients, hyperplasia in 39, and normal parathyroids in 26. Postoperatively there was a significant fall in serum calcium and urinary calcium excretion in all three groups. At clinical follow-up 2 to 5 years postoperatively there was no case of kidney stone recurrence among the adenoma patients. In the hyerplasia group there were recurrences tn 25 percent. The corresponding figure for the patients with normal parathyroids was 48 percent. The concept of normocalcemic primary hyperparathyroidism and the relationship between this syndrome and idiopathic hypercalciuria are discussed. Some prinicpal therapeutic measures are recommended.