During 1981, 946 patients with advanced renal failure who were maintained by dialysis were studied to assess the frequency and the duration of hospitalizations and to identify complications that prompted hospitalization. Five hundred fifty-eight patients (59%) were hospitalized for a total of 1,207 times (mean of 1.8 stays/yr and 15 days/yr at risk for the entire group). The major reasons for hospitalization were dialysis access problems (25%), gastrointestinal complications (13%), and cardiac complications (13%). Both the rate of stays/yr and the rate of days/yr increased with advancing age and were highest in patients who died during the year of study. Both the rate and the duration of hospitalization were higher for patients maintained by peritoneal dialysis than for those on hemodialysis (P less than 0.001). In patients younger than 45 years of age, diabetics had more frequent and more prolonged hospitalizations than nondiabetics, whereas in those 46 to 60 years of age, complications other than diabetes predisposed to hospitalization. In those 61 years of age or older, in whom hospitalization rates were the highest, no single risk factor could be identified as predisposing to hospitalization other than age and peritoneal dialysis. Although the interactions of these factors were not assessed, considerable agreement existed with previous studies that had been analyzed in a more sophisticated manner.