The authors correlated the dialysis parameters of 613 patients on hemodialysis with their morbidity and mortality. Dialysis prescription (Kt/V) was calculated according to the dialyzer, blood flow, and dialysis time. Dialysis delivered was calculated using percentage urea reduction (PUR). Eighty patients who underwent dialysis in three units had only predialysis blood urea nitrogen (BUN) values available. Mean predialysis BUN was between 58 +/- 16 and 83 +/- 17 mg/dl. Patients with predialysis BUN > 100 mg/dl ranged from 0-22%, and those with predialysis BUN < 50 mg/dl ranged from 0-41%. Kt/V prescribed was between 0.45 and 1.75. Mean dialysis time was 191 +/- 28 min, and blood flow was 327 +/- 48 ml/min. Delivered dialysis was 78% of that prescribed. Patients who had a prescribed or delivered Kt/V < 0.8 varied from 0-44.8%. Mortality rate per year was between 11.3% and 54%. The authors attributed elevated BUN to increased protein intake or inadequate dialysis. Low BUNs may have been due to residual renal function or malnutrition. None of the dialysis parameters correlated with mortality rate except for a Kt/V < 0.8 (p < 0.001) that was directly related to mortality rate. Inadequate dialysis increases mortality rate.