PURPOSE: This study was aimed to determine the predictive risk factors for the treatment response and relapse rate in children diagnosed with idiopathic nephrotic syndrome. METHODS: We analyzed the medical records of children who were diagnosed and treated for childhood idiopathic nephrotic syndrome from November 1991 to May 2005. Variables selected in this study were age at onset, sex, laboratory data, concomitant bacterial infections, days to remission, and interval to first relapse. RESULTS: There were 46 males and 11 females, giving a male:female ratio of 4.2:1. The age(mean+/-SD) of patients was 5.8+/-4.1 years old. Of all patients who were initially given corticosteroids, complete remission(CR) was observed in 54(94.7%). Of the 54 patients who showed CR with initial treatment, 40(70.2%) showed CR within 2 weeks and 14(24.6%) showed CR after 2 weeks. The levels of serum IgG were lower in the latter group who showed CR after 2 weeks(P=0.036). Of the 54 patients who showed CR with initial treatment, 47(82.5%) relapsed. Of these patients, 35.1% were frequent relapsers and 43.9% were infrequent relapsers. There was no significant correlation between the frequency of relapse and the following variables:sex, days to remission, and laboratory data. However, age at onset and interval to first relapse had a negative correlation with the frequency of relapse (Pearson's coefficient=-0.337, -0.433, P<0.012, P<0.01). CONCLUSION: The age at onset and the interval to first relapse were found to be predictive clinical parameters for the relapse rate, while the levels of serum IgG at initial presentation were a predictive laboratory factor for treatment response in childhood idiopathic nephrotic syndrome.