In the course of idiopathic nephrotic syndrome (INS), acute renal failure (ARF) may develop. The factors, which lead to ARF appearance are not entirely defined. In 1990-1997, 1006 children suffering from INS were admitted to our Department. ARF was noticed in 8 of them (0.8%), aged 6 to 17.5 years. The aim of study was to emphasize the clinical features of ARF and to evaluate factors that may contribute to renal failure in children with INS. The following data were considered: the course of INS (disease duration, the number of relapses, the remission periods), renal histology, degree of electrolyte disorders, lipid metabolism disorders, serum albumin level, intensification of proteinuria, presence of hypertension, applied treatment. According to the analysis, it seems that considerable hypoalbuminaemia, the presence of infection and severe course of nephrotic syndrome are the factors of ARF appearance risk in the course of INS.