The care of patients with acute renal failure remains a challenge for the nephrologist, with unacceptably high mortality rates. Among many other contributing factors, protein-calorie malnutrition has been suggested as an important predictor of outcome. Protein-calorie malnutrition is highly prevalent in acute renal failure (ARF) patients, and extensive catabolism is a hallmark of these patients. Hypercatabolism can be related to abnormal protein metabolism as well as be a consequence of renal replacement therapy. Inadequate nutritional supplementation also predisposes acute renal failure patients to poor nutritional status. Although multiple studies have evaluated the effects of aggressive nutritional supplementation to reverse malnutrition and improve the outcome in ARF patients, the complexity of the disease process has precluded obtaining meaningful and clear-cut results from these clinical studies. Nevertheless, there is a great need as well as potential to study the actual importance of nutritional aspects in complicated ARF patients.