Idiopathic(autoimmune) thrombocytopenic purpura(ITP) is characterized by thrombocytopenia and normal to increased numbers of megakaryocytes. ITP is a disease caused by circulating autoantibodies that react with the platelet membrane. It is thought that platelet-associated IgG(PAIgG) plays an important role in the mechanism of ITP, since increases in PAIgG are closely related to decreases in platelet count in patients with this disease. However, it is possible that PAIgG includes immune complex and platelet antibodies to human platelet alloantigens(HPA) other than autoantibodies. There have been several recent reports on autoantibodies to glycoprotein IIb/IIIa and Ib/IX. Although the etiology of ITP remains unclear, both genetic and environmental factors appear to be involved in it. With respect to the genetic aspects of ITP, the human leukocyte antigen (HLA) haplotype of patients is considered a potentially important factor in etiology. Various methods have been used for the treatment of chronic ITP. However, splenectomy and corticosteroids are still the mainstays of therapy. Because of the heterogeneity of the disease, however, approximately 20% of cases are refractory to these treatments. New therapy of chronic or refractory ITP with thrombopoietin, antiCD40 ligand antibody, and Helicobactor pylori eradication have recently been reported.