von Willebrand disease (vWD) is a common bleeding disorder characterized by quantitative or qualitative defects in von Willebrand factor (vWF), a protein important for coagulation and platelet adhesion. There are two forms of vWF currently recognized: plasma vWF synthesized by endothelial cells and platelet vWF produced within megakaryocytes. Although both plasma and platelet vWF play important roles in overall hemostasis, the relative contribution of each form is not clear.We report the results of bone marrow transplantation from a donor with Type I vWD into a hemostatically normal recipient.Following engraftment, the recipient appears to be a human chimera for vWD, with normal amounts of plasma vWF from endogenous endothelial cells, but low levels of platelet vWF derived from donor megakaryocytes.Although the vWD chimerism has not been associated with any clinical manifestations, the bleeding time has become prolonged, suggesting that platelet vWF is important for normalization of the bleeding time.