A patient with spontaneous hemorrhage from multiple body sites was found to have markedly prolonged international normalized ratio (INR) and activated partial thromboplastin times (aPTT) with incomplete correction of aPTT on mixing studies using normal plasma. The cause of this severe hemorrhage was due to a specific factor X inhibitor. No underlying or associated diseases were found. Initial treatment with fresh frozen plasma, vitamin K, and recombinant activated factor VII (rFVIIa) was unsuccessful. However, therapy utilizing plasma exchange with concomitant intravenous immunoglobulin and corticosteroids resulted in a rapid and sustained normalization of factor X levels with a clinical hemostatic response. Am. J. Hematol. 83:318-320, 2008. V