Two regimens of steroid treatment for the initial attack of idiopathic nephrotic syndrome in children were compared in a controlled multicentre study. Short-course prednisone therapy consisted of 60 mg/m2 per 24 h until proteinuria had disappeared for 3 days, followed by 40 mg/m2 per 48 h until complete remission had occurred. The standard prednisone therapy was 60 mg/m2 per 24 h for 4 weeks, followed by 40 mg/m2 per 48 h for 4 weeks. 61 children with a first attack of idiopathic nephrotic syndrome were allocated at random to these groups. Urinary remission in the short-course group was achieved after 14 days of daily prednisone, and complete remission after an additional 16 days of alternate day prednisone. The cumulative rate of patients with sustained remissions after two years was significantly lower after the short course than after standard treatment (19% versus 41%, p = 0.001). The mean duration of remission in patients with a relapse was half as long after the short course (79 versus 169 days, p = 0.004). Complete initial remission of steroid responsive nephrotic syndrome can be obtained with half the standard prednisone dose, but the short course is followed by a higher rate of relapses, that require repeated prednisone administrations. In the long term, the standard regimen is preferable.