Immune thrombocytopenic purpura (ITP) is an autoimmune disease mediated by anti-platelet autoantibodies. Recent accumulating evidence indicates that eradication of Helicobacter pylori (H pylori) is effective in increasing platelet count in nearly half of ITP patients infected with this bacterium. The H pylori eradication therapy for adult ITP is becoming very popular in Japan and is now chosen as an initial treatment in H pylori-infected patients. The lack of efficacy of the H pylori eradication regimen in H pylori-negative ITP patients clearly indicates that platelet recovery results from the disappearance of H pylori itself. Despite extensive efforts, clinical features characteristic to H pylori-related ITP and factors predicting the response after the H pylori eradication therapy have not been identified. Great variability in the efficacy of the H pylori eradication therapy in ITP patients exists among countries: a higher response rate has been found in Japan and Italy than in the United States and non-Italian European countries. Some children infected with H pylori show the platelet response after successful eradication of H pylori, but the H pylori eradication therapy is ineffective in patients with secondary ITP. The pathogenesis of ITP associated with H pylori remains obscure; the mechanisms are not simple and may involve multiple steps, including cross-reactivity between H pylori antigen and platelets, and suppression of the reticuloendothelial system. Further studies to evaluate the mechanisms responsible for the platelet response in ITP patients after successful eradication of H pylori may be useful in clarifying the pathogenesis of ITP and developing new therapeutic strategies for ITP.