Acute kidney injury (AKI), at least in critically ill patients, seldom occurs as isolated organ failure. Much more often it emerges as a component of the multiple organ failure syndrome, within the framework of the severe and prolonged catabolic phase determined by critical illness, and intensified by specific derangements in substrate utilization due to the acute loss of kidney function. On these bases, patients with AKI often have protein-energy wasting (preexisting and/or hospital acquired), which represents a major negative prognostic factor. Thus, nutritional support is frequently required, under the form of parenteral and/or enteral nutrition, even though no formal demonstration exists for its favorable effect on major outcomes. The primary goals of nutritional support in AKI are basically the same as those suggested for critically ill patients with normal renal function: i.e., to ensure the delivery of adequate amounts of nutrients, to prevent protein-energy wasting with the attendant metabolic complications, to promote wound healing and tissue reparation, to support immune system function and to reduce mortality. Patients with AKI on renal replacement therapy (RRT) should receive at least 1.5 g/kg per day of proteins, and no more than 30 kcal nonprotein calories or 1.3 x BEE (basal energy expenditure) calculated by the Harris-Benedict equation, with lipid supply representing about 30%-35% of energy. The enteral route should be the preferred route for nutrient delivery; however, parenteral nutrition is often required to target nutritional requirements. Due to the loss of the kidney's homeostatic function, and the frequent need of RRT, patients with AKI are especially prone to complications of nutritional support, such as hyperglycemia, hypertriglyceridemia, fluid retention, electrolyte and acid-base derangements. Since AKI comprises a highly heterogeneous group of subjects with nutrient needs widely varying even along the clinical course in the same patient, nutritional requirements should be frequently reassessed, individualized and carefully integrated with RRT.