The prevalence of Helicobacter pylori(H. pylori) infection and the effect of its eradication on platelet count in 51 chronic idiopathic thrombocytopenic purpura(ITP) and 9 secondary autoimmune thrombocytopenic purpura(SAITP) patients, were investigated. H. pylori infection was found in 31 ITP patients(60.8%) and in two SAITP(22.2%). H. pylori eradication was obtained in 24 of 26 infected ITP patients. 14 of 24 H. pylori-eradicated patients(58.3%) showed a significant increase in platelet count 6 months after eradication, however two infected patients with SAITP did not show platelet increase. This response was maintained in all responding patients throughout the follow-up period(median 20 months).