The aim of the research was to determine causes of acute renal failure in children, their outcome and to define risk factors associated with mortality. 75 children with acute renal failure, who were treated at the Clinic of Children's Diseases of Kaunas University of Medicine between 1998-2003 years, were included in the study. The age range of patients was 1 month to 16 years. They were divided into two groups. Acute renal failure was diagnosed in 42 (56%) patients (the first study group) and in 33 (44%) patients acute renal failure was together with multiple organ failure (the second study group). In the first study group 69% of cases of acute renal failure were found to be due to renal diseases and in the second study group 97% were because of extrarenal diseases. Sepsis was the most frequent cause of acute renal failure in the second group (p<0.02). Dialysis was made for 28% patients. Hypertension was diagnosed more often in the first patients group (p<0.05). Hypertension persisted in 9 (36%) patients after recovery. Chronic renal failure developed in two patients. 28 (37.3%) patients of the original study group died. Mortality rate for children with multiple organ failure was higher than for the children, who had renal insufficiency only (78.8% vs 4.8%; p<0.001). Mortality rate of infants in the first study group was higher than for children of the same age in the second group (p<0.001). Mortality rate for children, who had oliguria or anuria, was higher in the second group, too (p<0.001).