The occurrence of chronic renal insufficiency was investigated in 171 patients with severe idiopathic calcium stone disease. Ninety healthy subjects matched for age and sex were used as controls. The patients were thereafter subclassified into two subgroups, assuming a GFR of 80 ml/min/1.73 m<sup>2</sup> body surface area as a cut-off value: the normal GFR, 141patients, and the impaired GFR, 30 patients. The normal GFR group included more males and the patients were younger both at onset and at presentation. In the impaired GFR group the disease lasted longer, but the overall stones and the stone recurrence rate were as high as those of the normal GFR patients. The single stone episodes were more severe in the former group as suggested by the occurrence of more surgery and complications. The GFR level was in part predicted by the age of patients; however, stone disease was shown to induce a clear-cut influence in accelerating the natural worsening of GFR with age. The onset of renal insufficiency causes multiple changes in renal pathophysiology, which result in a sharp decrease in the urine saturation with respect to calcium salts. These changes account for the decrease in the stone recurrence rate in the impaired GFR group. Thus, unless factors independent of or complicating the calcium stone disease supervene, the renal insufficiency of treated patients remains mild and relently progressive.