The current study was designed first to determine separately the prescribed and delivered dose of dialysis and, second, to determine what factors lead to failure to deliver the prescribed dose of dialysis in patients with acute renal failure (ARF). Forty patients, who collectively underwent 136 dialysis treatments, were studied prospectively at two institutions. The results showed that almost half the prescriptions (49%) were for a Kt/V less than 1.2 and, more importantly, nearly 70% of the treatments delivered a Kt/V less than 1.2, the minimally acceptable dose defined in the Dialysis Outcomes Quality Initiative (DOQI) guidelines for chronic hemodialysis (CHD) patients. Patient predialysis weight was the most important variable associated with a low prescribed and delivered dose of dialysis, as well as lack of delivery of the prescribed dose of dialysis. From the statistical model, it is estimated that for every 10-kg increase in predialysis weight, the chance of prescribing or delivering a Kt/V less than 1.2 increased 4.6- and 1.95-fold, respectively. The lower than prescribed blood flow achieved by the temporary catheters and patients not receiving anticoagulation were variables also associated with not receiving the prescribed Kt/V. It is concluded that patients with ARF are prescribed and receive a dose of dialysis that would be considered inadequate for CHD patients. Until the association between dose of dialysis and outcome is better defined, it would be prudent that both the dialysis prescription and the delivery of dialysis to patients with ARF should be performed with the same care and goals as that currently received by patients with end-stage renal disease (ESRD).