In its classic presentation, the antiphospholipid syndrome manifests a combination of venous or arterial thrombosis and fetal loss, accompanied by elevations of antibodies directed toward negatively charged phospholipids, as measured by anticardiolipin antibody assays and/or positive lupus anticoagulant tests. The manifestations often include a moderate thrombocytopenia and, less commonly, hemolysis. In contrast, a less frequently encountered subset of the antiphospholipid syndrome, termed the "catastrophic" antiphospholipid syndrome, affects mainly small vessels predominantly supplying organs. The thrombocytopenia is usually marked, and a Coombs positive microangiopathic-type anemia may accompany the condition. Features of disseminated intravascular coagulation may be evident in some patients. It is fatal in approximately 50% of cases reported. Treatment should include not only adequate anticoagulation with intravenous heparin but also full doses of intravenous corticosteroids, to offset the systemic inflammatory response syndrome that occurs as a result of the extensive tissue damage, and plasmapheresis, using fresh frozen plasma. Parenteral antibiotics should be administered early if infection is suspected.