To define factors of prognostic importance for critically ill infants and children with acute kidney injury (AKI), we have studied 110 children, ages from 1 month to 180 months, admitted between March 1, 2002 and September 30, 2004 to the intensive care unit of Joana de Gusmão Children's Hospital. These patients represent 8% of all intensive care unit admissions during the entire study period. The diagnosis at admission was primary renal parenchyma disease (eight patients, 7.2%) and secondary renal disease (102 patients, 92.8%). Thirty-seven patients (33.6%) died, all of whom had secondary renal insufficiency; six patients (5.4%) died as a result of septic shock, and 31 (28.2%) patients died from multiple organ failure (MOF). The variables were analyzed using Fisher's exact test for qualitative variables and Student's t-test for quantitative variables. Stratified analysis was performed to assess the relative importance of variables using the Mantel-Haenszel technique. Among the variables analyzed, the following were found to be significantly related to mortality: anuria, oliguria, arterial hypotension, need for pressor drugs, need for mechanical ventilation, need for dialysis, the association with MOF, and high values of lactic acid.