The nutritional support of patients with acute renal failure (ARF) in the ICU has undergone major changes. Nutritional therapy in these patients should not depend on the impairment of renal function but on the severity of multiple organ failure (MOF). There are no differences in general rules for the nutrition of the critically ill with or without ARF. Because ARF, per se, does not affect energy expenditure, energy requirements in these patients are the same as in other MOF patients. Thirty to 35 kcal/kg/day should be administered as carbohydrate and lipid solutions, and the serum concentration of glucose and triglycerides controlled. In contrast to patients with chronic renal failure, in ARF patients nitrogen administration of approximately 1.5 to 1.7 g amino acids/kg/day is necessary to diminish protein catabolism. No clinical data exist about the best composition of the administered amino acids, but a mixture of essential and nonessential amino acids seems sensible; the exclusive administration of essential amino acids is obsolete. New dialysis techniques such as continuous renal replacement therapy offer the opportunity to adapt nutrition to each individual patient's needs. Using these techniques, there is no reason to reduce nutrition because of fluid restriction, as is often necessary in intermittent hemodialysis.