We identified 55 patients with dialysis encephalopathy in six dialysis centers studied by means of a uniform clinical classification. Dialysis encephalopathy was the direct cause of death in most cases, and the disease appeared to significantly shorten survival. The overall attack rate of dialysis encephalopathy was 4% and varied among dialysis centers from 2.2% to 14.7%. In two centers with adequate data, the attack rate for dialysis encephalopathy rose significantly with increasing cumulative aluminum exposure via dialysate, and the mean cumulative aluminum exposure for patients with the disease was significantly higher than that for all other patients at risk. We further demonstrated that the cumulative level of aluminum tolerated by the patient before onset of symptoms was inversely related to the average aluminum concentration of dialysate water.