Prevalence of renal insufficiency and renal failure of newborns in an intensive care unit is considerably high. Most patients have prerenal failure which is associated with the underlying disease, some have had heart surgery and only few patients have congenital renal malformation. In a retrospective analysis in our institution main risk factors were: prematurity, age < 10 days, obstetric complications, male gender, Cesarean delivery and pulmonary disease. We could not confirm, however, that asphyxia is significant for renal failure. Much more common than manifest renal failure is renal insufficiency in diseased newborns during intensive care. The cause is sometimes primary renal insufficiency as a harbinger of renal failure, but it is often iatrogenic, because fluid intake is inadequate, either unintentional or for a purpose. This strategy, however, conflicts with a conservative approach to renal insufficiency, which requires adequate fluid and caloric intake. A skilled approach to this situation demands a daily re-evaluation of the fluid regimen with regard to possible liberalization. If renal failure progresses dialysis may be indicated, but this remains controversial in neonates. However, with growing expertise, skill and adequate equipment, different techniques of dialysis nowadays can be applied even to small infants. Mortality in infants with acute renal failure ranges from 25 to 78%, but death is seldom caused primarily by renal disease. In our survey 0.9% in a total of 34% mortality was attributed to renal disease. Attention has to be paid to the bulk of diseased newborns, who experience only slight increase in serum creatinine in their early life with only mild (or even without) oliguria, who may be prone to residual renal morbidity as well as those, who have manifest renal failure.