Thrombocytopenia-associated multiple organ failure (TAMOF) is a poorly understood syndrome in critically ill children. ADAMTS-13, formerly known as von Willebrand factor (VWF) cleaving protease, is decreased in adults with VWF mediated thrombotic microangiopathy, and intensive plasma exchange (PEx) both replenishes ADAMTS-13 and improves outcome in these patients. We hypothesized that children with TAMOF syndrome have decreased ADAMTS-13 activity which can be replenished with PEx. In the first of two consecutive studies, relationships between platelet count, VWF multimers, ADAMTS-13 activity, plasminogen activator inhibitor-1 (PAI-1) and prothrombin time (PT) were analyzed in children with and without TAMOF. In the second study, children with severe TAMOF (platelet counts<100,000/mm3 and ≥3 organ failure) were randomized to PEx or standard therapy. In the first study, children with TAMOF (n=28) had decreased ADAMTS-13 activity, but similar PAI-1 activity and PT compared to children with MOF without thrombocytopenia (n=9) (p<0.05). All non-survivors (n=7) had TAMOF, reduced ADAMTS 13 activity, and VWF-rich microvascular thromboses at autopsy. In the second study, PEx (n=5, median 12 days, 4–28 days) restored ADAMTS-13 activity and organ function, compared to standard therapy (n=5) (p<0.05). Children with TAMOF syndrome can have VWF mediated thrombotic microangiopathy. Similar to adult experience, PEx can replenish ADAMTS-13 activity and reverse organ failure in these children.