Two groups of patients are admitted in the pediatric ICU with renal problems. The first and more common is the one, who develops renal failure secondary to multiorgan disease. The second group is the one, who is admitted to PICU for primary renal disease, acute or chronic. In both situations, the patients develop fluid and electrolyte imbalance. As a result, the patients can potentially develop life-threatening complications that need to be taken care of in the pediatric intensive care unit. The incidence of acute renal failure (ARF) in the PICU is extremely variable. The occurrence of ARF in any single PICU depends on the type of patients being taken care of in that particular unit. The incidence will be higher in any unit taking care of children following cardiac surgery, since the incidence of ARF in that patient group can be as high as 8%.