Antiphospholipid antibodies are a relatively heterogeneous mix of immunoglobulins with binding specificities for negatively charged or neutral phospholipids. Currently, the most commonly detected antiphospholipid antibodies include the anticardiolipin antibody, the lupus anticoagulant, and an antibody implicated in false-positive VDRL testing. Recently, a clinical syndrome of vaso-occlusive disorders associated with antiphospholipid antibodies has been identified and may result from immune-mediated disruption of endothelial function. This clinical syndrome encompasses arterial and venous thrombosis, recurrent fetal loss, neurologic dysfunction (eg, migraine, chorea, and encephalopathy), systemic and pulmonary arterial hypertension, and endocardial disease. Although most commonly associated with systemic lupus erythematosus, the antiphospholipid antibody syndrome also has been identified in patients with vaso-occlusive disease without systemic lupus erythematosus. Recently, identification of antiphospholipid antibodies has been facilitated by the development of a more sensitive assay for anticardiolipin antibody. In this article, case histories of three patients with arterial thrombosis and associated anticardiolipin antibodies, including the first associated case of terminal aortic thrombosis, are reviewed and the subject of the antiphospholipid antibody syndrome is discussed.