The evolution of renal stone disease has been followed, before and after parathyroidectomy, in 197 patients with primary hyperparathyroidism. Before operation, 120 patients had had a previous history of renal colics or stones, or both, demonstrated on roentgenograms of the urinary tract. In 36 patients with stones that had been passed or removed before exploration of the neck, no recurrence of lithiasis has been observed. In 84 patients who still had stones at the time of the operation, the stones dissolved and disappeared within ten years in 88 per cent of those with urolithiasis and in 77 per cent with nephrocalcinosis. The rate of stone disappearance was similar in those with or without preoperative urinary tract infection and in patients operated upon for adenoma of the parathyroid gland or primary hyperplasia. This rate was slower for patients with a postoperative urinary infection. The frequency of renal colics, 0.66 per patient per year before parathyroidectomy, decreased to 0.02 per patient per year after the first postoperative year.