Antibodies directed against phospholipids are highly associated with venous and arterial thrombotic episodes, which are often recurrent. There seems to be a skewed frequency of cerebral and ocular events when the arterial circulation is affected. Other neurologic syndromes, including dementia, migraine, chorea, transverse myelopathy, Guillain Barré syndrome, transient global amnesia, seizures, motor neuron disease, myasthenia gravis, and depression, have also been described in association with aPL. Although some of them (for example, dementia, chorea, seizures, and transient global amnesia) could well be the result of aPL-related cerebrovascular disease, the relationship of aPL to the underlying pathophysiology of these syndromes is less clear. Clues that should lead one to consider evaluating for these antibodies include recurrent thrombosis (especially in young people), recurrent fetal loss, and thrombocytopenia. Associated laboratory abnormalities may include a biologically false-positive VDRL test, abnormal ANA or anti-DNA titers, and a high ESR. If the APTT is positive on routine screening and does not correct with mixing studies, a LA should be highly suspected. More sensitive and specific tests are usually necessary to detect aPL, however. Many in vitro and, more recently, in vivo systems strongly suggest that aPL may be directly implicated in the pathogenesis of thrombosis, as opposed to being markers of a procoagulant state. The management of patients with aPL-associated thrombosis can be difficult. Prospective studies are needed to determine the optimal treatment strategies for this group of patients.