Death rates of end-stage renal disease (ESRD) patients treated with hemodialysis vary substantially among treatment centers. The association between facility-to-facility differences in delivered hemodialysis dose and facility-specific mortality rates was examined among 5817 randomly selected patients treated with hemodialysis on October 1, 1994, from all 213 hemodialysis treatment centers reporting to ESRD Network 6. The mean urea reduction ratio (URR) for each treatment center, a measure of hemodialysis adequacy, was calculated for each facility, using measurements made by center staff members during one treatment for each of the randomly selected patients. During 7 mo of follow-up (ending April 30, 1995), 441 (7.6%) patients died. The average URR among the treatment centers was 64.9%. There was a strong, inverse association between increasing treatment center URR and adjusted mortality count (P = 0.009). Other treatment center characteristics associated with increased mortality included free-standing status (P = 0.009) and decreasing frequency of reported physician supervision of care (P = 0.01). It was concluded that lower average levels of dialysis adequacy in treatment centers are associated with higher rates of death, and this association persists after controlling for facility-to-facility differences in patient and nonpatient characteristics.