Acute renal failure (ARF) in children has a poor prognosis in spite of modern therapeutic techniques. For this reason, it would be useful to have prognostic indicators early in the course of the disease, in order to identify those patients that could benefit most from aggressive treatment. In an attempt to establish valid prognostic factors, we prospectively studied 138 cases of ARF in children. We examined age, sex, etiology of ARF, previous surgery, prerenal origin, clinical situation of the patient when first seen by the nephrologist and complications. All these variables were statistically analyzed individually by univariate tests and, except for sex and complications, also by multiple regression analysis. Median age of the patients was 26 months. The etiology of ARF was nephropathy in 16, tumor in 14, cardiopathy in 85 and other causes in 23 cases. For analysis, patients were divided into patients with and without prerenal ARF. In the prerenal group, mortality-related factors were hypotension, need for ventilatory support, age less than 1 month and serum values of creatinine. In the nonprerenal ARF group, the need for assisted ventilation and the need for dialysis correlated positively with the mortality, while an exclusive nephrological etiology was associated with less probability of death.