Renal failure commonly occurs in an ICU as part of the evolution of an underlying disease process. Appropriate and rapid resuscitation and treatment prevents or reverses prerenal insults. Patients usually make a complete recovery if the disease process is reversible and the renal injury mild or moderate. More severe degrees of renal injury initially require conservative management with attention to maintaining a diuresis, preventing fluid, electrolyte, and acid-base imbalances, and ensuring adequate nutrition. Renal replacement therapy is required for the more severe forms of renal failure. Continuous forms of RRT are gaining favor as they are associated with less hemodynamic instability, though current evidence does not demonstrate any clear outcome benefit. Mortality is high when the severe form of ARF is established. ARF may have some attributable mortality, but the poor outcome is usually related more to the underlying medical problems and concurrent multisystem derangements.