Antiphospholipid antibodies (aPL) occur in a variety of autoimmune, malignant, and infectious diseases, with or without the thrombotic or obstetric sequelae that characterize the antiphospholipid syndrome. Although many studies have focused on the clinical implications of aPL in systemic lupus erythematosus, few have specifically addressed the questions facing rheumatologists caring for rheumatoid arthritis patients who are concomitantly positive for aPL. Such a clinical scenario requires current knowledge of antiphospholipid syndrome diagnosis criteria, test reliability, conditions causing temporal positivity of aPL, and treatment risks and benefits. Recently researched factors possibly integral to rheumatoid arthritis's increased morbidity and mortality and related to aPL include oxidatively modified low-density lipoprotein antibodies, homocysteine, annexins, infectious agents, beta estradiol, and specific gene polymorphisms. This review presents current scientific research addressing the pathophysiologic mechanisms and clinical implications of aPL in rheumatoid arthritis.