Henoch-Schönlein purpura (HSP) is the one of most common types of systemic vasculitis in childhood. Glomerulonephritis (HSPN) occurs in 30-50 % of HSP patients, mostly in a mild form but a small percentage of patients present with nephrotic syndrome or renal failure. HSPN is caused by the glomerular deposition of immunoglobulin A1 (IgA1)-containing immune complexes in the mesangium, the subepithelial and the subendothelial space. Formation of the IgA1 immune complex is thought to be the consequence of aberrantly glycosylated IgA1 molecules secreted into the circulation and their subsequent recognition by IgG specific for galactose-deficient IgA1. Mesangial proliferation and renal damage are triggered by the deposited immune complexes, which likely require activation of the complement system. Whereas other organ manifestations of HSP are mostly benign and self-limiting, HSPN might lead to chronic renal disease and end stage renal failure, thereby justifying immunosuppressive treatment. Long-term renal outcome correlates to the severity of the initial clinical presentation and the extent of renal biopsy changes, both of which are used to decide upon a possible treatment. As there are no evidence-based treatment options for severe HSPN, a large variety of therapeutic regimens are used. Prospective randomized controlled treatment studies are needed, but the low incidence of severe HSPN renders such studies difficult.