Acquired von Willebrand syndrome (AVWS) is a rare bleeding disorder with laboratory findings similar to those for congenital von Willebrand disease. Unlike the congenital form, AVWS usually occurs in individuals with no personal or family history of bleeding disorders. According to an international registry, AVWS is mainly associated with lymphomyeloproliferative, immunologic, and cardiovascular disorders, as well as with solid tumors and other miscellaneous conditions; however, the prevalence of AVWS in these underlying disorders is still unknown. von Willebrand factor (VWF) is synthesized normally in most AVWS patients, and the low plasma VWF levels are from its accelerated removal from plasma by five different mechanisms, including autoantibodies. Because of the reduced half-life of endogenous-exogenous plasma VWF, bleeding of AVWS cannot be managed with desmopressin or factor VIII/VWF concentrates. Clinical use of intravenous immunoglobulin (IVIg) in AVWS has been reported since 1988. IVIg is most effective in AVWS with type immunoglobulin (Ig) G monoclonal gammopathies of undetermined significance and in other cases with IgG autoantibodies. IVIg can correct factor VIII and von Willebrand factor complex activities for about 15-20 days, and repeated injections induce remission of AVWS in these patients. Prospective studies are required to evaluate the efficacy and safety of IVIg in AVWS.