An episode of gastroenteritis triggered severe necrosis of all extremities in a previously asymptomatic male. Hepatic and renal involvement were also manifest, while the hematological picture was one of thrombotic microangiopathic hemolytic anemia. Antiphospholipid antibodies were negative. He responded well to a combination of plasma exchange, anticoagulation (heparin), parenteral steroids, and antibiotics, as well as vasodilators (prostacycline) and hyperbaric oxygen, but died because of a cerebral hemorrhage. The differential diagnosis included thrombotic thrombocytopenic purpura/hemolytic-uremic syndrome, or seronegative catastrophic antiphospholipid (Asherson's) syndrome. The dangers of administering such a combination of therapies with anticoagulation, as well as vasodilatation (prostacycline) and hyperbaric oxygen, are highlighted by the case report and emphasized.