Background: Henoch-Schönlein purpura (HSP) is the most common vasculitis of childhood but may occur in adults. This small vessel vasculitis is characterised by palpable purpura, abdominal pain, arthritis or arthralgia and kidney involvement. This is an update of a review first published in 2009. Objectives: To evaluate the benefits and harms of different agents (used singularly or in combination) compared with placebo, no treatment or any other agent for: (1) the prevention of severe kidney disease in patients with HSP without kidney disease at presentation; (2) the prevention of severe kidney disease in patients with HSP and minor kidney disease (microscopic haematuria, mild proteinuria) at presentation; (3) the treatment of established severe kidney disease (macroscopic haematuria, proteinuria, nephritic syndrome, nephrotic syndrome with or without acute kidney failure) in HSP; and (4) the prevention of recurrent episodes of HSP-associated kidney disease. Search methods: We searched the Cochrane Kidney and Transplant's Specialised Register to 13 July 2015 through contact with the Trials Search Co-ordinator using search terms relevant to this review. Selection criteria: Randomised controlled trials (RCTs) comparing interventions used to prevent or treat kidney disease in HSP compared with placebo, no treatment or other agents were included. Data collection and analysis: Two authors independently determined study eligibility, assessed risk of bias and extracted data from each study. Statistical analyses were performed using the random effects model and the results were expressed as risk ratio (RR) or risk difference (RD) for dichotomous outcomes and mean difference (MD) for continuous outcomes with 95% confidence intervals (CI). Main results: Thirteen studies (1403 enrolled patients) were identified. Risks of bias attributes were frequently poorly performed. Low risk of bias was reported in six studies (50%) for sequence generation (selection bias) and in seven (58%) for allocation concealment (selection bias). Blinding of participants and personnel (performance bias) and of outcome assessment (detection bias) was at low risk of bias in three studies. Five studies reported complete outcome data (attrition bias) while eight studies reported expected outcomes so were at low risk of reporting bias. Eight studies evaluated therapy to prevent persistent kidney disease in HSP. There was no significant difference in the risk of persistent kidney disease any time after treatment (5 studies, 746 children: RR 0.74, 95% CI 0.42 to 1.32), or at one, three, six and 12 months in children given prednisone for 14 to 28 days at presentation of HSP compared with placebo or supportive treatment. There were no significant differences in the risk of persistent kidney disease with antiplatelet therapy in children with or without kidney disease at entry. Heparin significantly reduced the risk of persistent kidney disease by three months compared with placebo (1 study, 228 children: RR 0.27, 95% CI 0.14 to 0.55); no significant bleeding occurred. Four studies examined the treatment of severe HSP-associated kidney disease. Two studies (one involving 56 children and the other involving 54 adults) compared cyclophosphamide with placebo or supportive treatment and found no significant benefit of cyclophosphamide. There were no significant differences in adverse effects. In one study comparing cyclosporin with methylprednisolone (15 children) there was no significant difference in remission at final follow-up at a mean of 6.3 years (RR 1.37, 95% CI 0.74 to 2.54). In one study (17 children) comparing mycophenolate mofetil with azathioprine, there was no significant difference in the remission of proteinuria at one year (RR 1.32, 95% CI 0.86 to 2.03). No studies were identified which evaluated the efficacy of therapy on kidney disease in participants with recurrent episodes of HSP. Authors' conclusions: There are no substantial changes in conclusions from this update compared with the initial review. From generally low quality evidence, we found no evidence of benefit from RCTs for the use of prednisone or antiplatelet agents to prevent persistent kidney disease in children with HSP. Though heparin appeared effective, this potentially dangerous therapy is not justified to prevent serious kidney disease when fewer than 2% of children with HSP develop severe kidney disease. No evidence of benefit has been found for cyclophosphamide treatment in children or adults with HSP and severe kidney disease. Because of small patient numbers and events leading to imprecision in results, it remains unclear whether cyclosporin and mycophenolate mofetil have any roles in the treatment of children with HSP and severe kidney disease.