Acquired von Willebrand syndrome (AVWS) is a rare bleeding disorder similar to inherited von Willebrand disease. We describe a 78-year-old woman with coexistent idiopathic thrombocytopenic purpura (ITP) and AVWS. The patient had once been admitted to our hospital because of cerebral infarction. Her platelet count had been normal at that time. Ten years later, she showed a severe bleeding tendency (platelet count 3.2×10(4)/μl). Analysis of hemostatic parameters showed very low (<6%) von Willebrand factor ristocetin cofactor (vWF: Rco), and low VIII: C (22%), but elevated (276%) von Willebrand antigen. Electrophoretic analysis of plasma showed low levels of the high-molecular weight VWF multimer. The presence of antibodies (IgG1 and IgG4) to VWF was detected by enzyme linked immunosorbent assay (ELISA). Factor XIII activity was 42%. Treatment with corticosteroids did not improve the thrombocytopenia, but did correct the bleeding diathesis. Also, VWF: Rco and VIII: C showed normalization. These findings indicated that the patient had ITP associated with AVWS. All reported cases of AVWS associated with systemic lupus erythematosus were cured by appropriate treatment of the underlying autoimmune disease with prednisone or immunosuppression. This bleeding disorder occurs mainly in patients with lymphoproliferative, myeloproliferative, cardiovascular and immunologic disorders, but no patients with ITP have previously been reported. This patient had the rare presentation of AVWS complicated by ITP and factor XIII deficiency.