Immune thrombocytopenic purpura (ITP) is associated with cytokine response and dysregulation of the cytokine network. We investigated the polymorphisms of interleukin (IL)-1beta exon 5 and IL-1 receptor antagonist (IL-1 Ra) in 50 children with acute ITP, in 30 children with chronic ITP, and in 100 healthy children by polymerase chain reaction-based restriction analysis. No significant differences in either genotype distribution (P=0.52) or allelic frequencies (P=0.70) were found among children with acute ITP, chronic ITP, or controls for IL-1beta exon 5. However, significant differences in genotype distribution (P=0.02) and the allelic frequencies (P=0.007) were found among children with acute ITP, chronic ITP, and controls for IL-1 Ra. We found that the IL-1 Ra but not IL-1beta gene polymorphism was associated with childhood ITP. This finding suggests that the IL-1 Ra gene polymorphism is implicated in the pathophysiology of childhood ITP.