Four patients with isolated acute ocular ischemic syndromes also had circulating antiphospholipid antibodies. Two patients had vaso-occlusive retinopathy and two, anterior ischemic optic neuropathy (which was successive in one). Extensive clinical laboratory evaluation identified vascular risk factors in two patients. One patient had essential thrombocytosis, confirmed by bone marrow biopsy; the other had stable hypertension and a history of coronary artery disease. These cases suggest that small vessel thrombosis in situ may be a mechanism for antiphospholipid-associated ocular and cerebral ischemia.