Release of unusually large von Willibrand factor (UL v WF)vmultimers and a deficiency of vWF metalloprotease may result in thrombotic thromocytopenic purpura (TTP), a life threatening disease. Surgery has been associated with TTP, probably by releasing massive amounts of UL v WF. An association bwteeen TTP and orthopedic surgery has never been reported inthe literature. We report a case of TTP following a total knee replacement surgery in which prior use of ticlopidine mighthave played a role.