To determine the impact of a quality improvement intervention on dialysis care delivered to hemodialysis patients, we studied 213 hemodialysis facilities in North Carolina, South Carolina, and Georgia. Dialysis adequacy measurements made on two random samples of 30 patients per treatment center, or all patients if fewer than 30 were treated, selected in October 1994 (preintervention) and October 1995 (postintervention) were used to estimate the facility mean urea reduction ratio (URR) and the proportion of patients with a mean URR less than 50%. The 10% of facilities (n = 22) with the highest proportion of patients with a mean URR less than 50% in the facility at preintervention were selected for an intervention that included feedback of facility-specific mean URR, educational programs, a quality improvement workshop, and monitoring until improvement was attained. Changes between preintervention and postintervention facility mean URR and proportions of patients with a URR less than 60% and 65% were used to assess the impact of the intervention. After 1 year, the mean URR had increased an average of 7% in intervention centers compared with an increase of 1.4% (P < 0.001) in the remainder of the treatment centers in the Network. There was an average reduction of 17.2% in the proportion of patients with a URR less than 65% in intervention centers compared with 4.8% in the other facilities (P < 0.001). Comparable reductions in the proportion of patients with a mean URR of less than 60% were 16.2% in intervention centers and 2.0% in comparison facilities (P < 0.001). After controlling for facility case mix and other characteristics, the intervention was independently associated with an absolute 2.4% increase in facility-specific mean URR. We conclude that the intervention was associated with improvement in hemodialysis care.