PURPOSE To further define familial infantile thrombotic thrombocytopenic purpura and clarify its pathophysiology, we describe a family with two infants presenting with this rare syndrome. RESULTS Complete, but temporary remission followed the transfusion of whole blood in the first sibling and fresh frozen plasma (FFP) in the second. Periodic FFP transfusions have kept the surviving proband in a prolonged clinical remission. The presence of unusually large von Willebrand factor multimers was demonstrated in the proband and the processing activity of these large multimers was found to be normal. CONCLUSION The occurrence of this rare disorder, in siblings who are products of a consanguinous union, suggests an as yet uncharacterized genetic defect.