The pathogenesis of Henoch-Schönlein purpura (HSP) remains unknown; however, it is generally considered to be an immune complex-mediated disease. Cytotoxic T lymphocyte-associated protein 4 (CTLA-4) is expressed on activated T cells, and, thus, it is critically involved in the immune response. We aimed to investigate the possible influence of CTLA-4 polymorphisms for susceptibility to HSP and determine if there were associations with human leukocyte antigen (HLA)-DRB1 genotypes. Using polymerase chain reaction-based DNA genotyping, we investigated the polymorphisms located in the genes encoding CTLA-4 in 100 patients with HSP and 156 ethnically matched healthy controls. When CTLA-4 +49 A/ G polymorphism of HSP patients and control group was compared, no associations with joint, gastrointestinal or renal manifestations, or susceptibility to HSP, were observed. However, patients with nephrotic proteinuria had higher HLA-DRB1*13 positivity [odds ratio (OR)=3.76, 95% confidence interval (95%CI)=1.25-11.23, P=0.025]. When the patients were stratified according to CTLA-4 polymorphism, a significant association between nephrotic proteinuria patients and carriage of the AG genotype was also found (OR=15.42, 95%CI=1.59-148.82, P=0.008). These results suggested that CTLA-4 +49 A/G polymorphism does not contribute to susceptibility to HSP; however, the presence of CTLA-4 AG genotype and HLA-DRB1*13 could be a risk factor for developing nephrotic-range proteinuria in these patients. © IPNA 2008.