Objective To identify early prognostic factors for idiopathic nephrotic syndrome (INS) in childhood. Study design A retrospective analysis of 103 patients with INS at onset, all treated in a single center with the same induction protocol, was conducted. Minimum length of follow-up was 2 years; median length of follow-up was 43 months. Survival data were assessed with Cox-Mantel analysis. Predictive values were estimated with receiver operating characteristic curves. Results The median time of response to steroid therapy was 7 days. A significant association was found between the interval from onset of steroid therapy to remission and the risk of relapsing within 3 months after steroid therapy discontinuation ( P < .0001). A similar association was found between the time to achieve remission and the risk of developing frequent relapsing or steroid-dependent nephrotic syndrome ( P < .0001), the prescription of maintenance steroid therapy ( P < .003), and the prescription of all other non-steroid drugs ( P < .0001) during follow-up. Patients with non-relapsing and infrequent relapsing nephrotic syndrome had a median time to achieve remission <7 days; in patients with frequent relapsing and steroid-dependent nephrotic syndrome, this median was >7 days. Conclusion The interval from onset of steroid therapy to remission is an accurate early prognostic factor in INS.