Antibodies to negatively charged phospholipids (aPL) are associated with a wide clinical spectrum. Primarily the clinical problems present as localized and/or generalized thromboses, recurrent fetal loss, strokes, and various cytopenias. The clinical settings which would prompt the physician to consider aPL as causal or contributory to pathology in many organ systems are reviewed, and guidelines for screening and confirmatory testing are defined. Since effective treatments do exist to decrease or prevent morbidity, and in some cases, mortality, the generalist as well as the specialist should be aware of the many faces these primary and secondary syndromes present to them in daily practice.