BACKGROUND In nephrotic syndrome protein leaks from the blood to the urine through the glomeruli resulting in hypoproteinaemia and generalised oedema. About 70% of children experience a relapsing course with recurrent episodes of oedema and proteinuria. Children with untreated nephrotic syndrome frequently die from infections. The majority of children with nephrotic syndrome respond to corticosteroids. Corticosteroid usage has reduced the mortality rate in childhood nephrotic syndrome to around 3%, with infection remaining the most important cause of death. However corticosteroids have known adverse effects such as obesity, poor growth, hypertension, diabetes mellitus and osteoporosis. The original treatment schedules for childhood nephrotic syndrome were developed in an ad hoc manner. The optimal doses and durations of corticosteroid therapy that are most beneficial and least harmful have not been clarified. The aim of this systematic review is to assess the benefits and harms of corticosteroid therapy in treating children with nephrotic syndrome. OBJECTIVE To determine the benefits and harms of different corticosteroid regimes in preventing relapse in children with steroid responsive nephrotic syndrome (SRNS). METHODS Published and unpublished randomised controlled trials were identified from the Cochrane Controlled Trials Register, Medline, Embase, reference lists of articles, abstracts from proceedings and contact with known investigators in the area. METHODS Randomised trials were included if they were carried out in children (aged three months to 18 years) in their initial or subsequent episode of SRNS, if they compared different durations, total doses or other dose strategies using prednisone or other corticosteroid agent and if they had outcome data at six months or more. METHODS Two reviewers independently reviewed all eligible studies for inclusion, assessed study quality and extracted data. The principle outcome measure was the number of children with and without relapse after six and 12-24 months. Secondary outcomes sought included the number of children who developed frequently relapsing nephrotic syndrome and adverse events. A random effects model was used to estimate summary effect measures (relative risk RR, risk difference RD) after testing for heterogeneity. Meta-regression was used to explore potential between-study differences due to the baseline risk of relapse, study quality and types of interventions used. RESULTS Twelve trials were identified. A meta-analysis of five trials, which compared two months of prednisone with three months or more in the first episode, showed that the longer duration significantly reduced the risk of relapse at 12 - 24 months (relative risk 0.73; 95% CI 0.60,0.89) without an increase in adverse events. There was an inverse linear relationship (RR = 1.382 (SE 0.215) - 0.133 duration (SE 0.048); r2 = 0.66; p = 0.05) between the duration of treatment and risk of relapse. The number of children who became frequent relapsers and the mean relapse rate/patient/year were also significantly reduced without increase in serious adverse events. In children with frequently relapsing nephrotic syndrome, deflazacort was significantly more effective in maintaining remission than prednisone (RR 0.44; 95% CI 0.25, 0.78). CONCLUSIONS From this meta-analysis of randomised controlled trials it can be concluded that children in their first episode of nephrotic syndrome should be treated for at least three months with an increase in benefit being demonstrated for up to seven months of treatment. In a population with a baseline risk for relapse following the first episode of 60% with two months of prednisone, daily prednisone for four weeks followed by alternate day therapy for six months would be expected to reduce the number of children experiencing a relapse by about 40%. In children who relapse frequently, deflazacort deserves further study.