The results from a prospective study of 100 cases of acute renal failure in children with cardiopathy are presented. 72 underwent surgery before the acute renal failure. Mean age was 33 months +/- 54 and median age was 6 months. Overall mortality was 50 %. In order to establish prognostic factors, we have analyzed several aspects: Age, sex, etiology of acute renal failure, complexity of the cardiopathy, previous surgery, clinical situation of the patient when the nephrologist saw him for the first time, pre-renal situation, existence of acute tubular necrosis, complications and causes of death, separately by univariate analysis, and all above mentioned items, except sex, etiology, complications and causes of death by a multiple linear regression analysis. Complexity of the cardiopathy, need of mechanical ventilation and dialysis, oliguria and acute tubular necrosis correlated positivel with mortality.