Dialysis time is increasingly being appreciated as an important measure of dialysis adequacy. Increased dialysis time leads to better control of volume excess, to reduced occurrence of intradialytic hypotension, and to better control of serum phosphorus. Nevertheless, the amount of benefit obtainable by moderate increases in dialysis time in patients following a three-times-per-week schedule has not been well established, and the analysis is confounded by associations between prescribed and/or delivered dialysis time and factors related to patient mortality.