Abstract
Circulating anticoagulants are endogenous blood components that inhibit the action of clotting factors. In some inhibitor conditions this inactivation in the function of the hemostatic system may lead to life-threatening hemorrhagic diathesis. Inhibitors directed against factor XI are generally associated with little or no impairment of the hemostatic system. All reported cases of spontaneous factor XI inhibitor were analyzed in the international literature, as well as other cases identified considering clinical spectrum, diagnosis and therapy.