Summary. Acquired factor VIII inhibitor causes a rare but life-threatening form of bleeding disorder, owing to the formation of auto-antibodies against FVIII. Treatment modalities include the use of immunosuppressive drugs such as cyclophosphamide and corticosteroids, plasmapheresis and i.v. immunoglobulin. A patient with idiopathic acquired FVIII inhibitor presented with serious bleeding complications resistant to all the above therapeutic modalities. Treatment with cyclosporin, however, resulted in a prompt and complete response. The lack of side-effects and the relatively quick response suggest that cyclosporin may be tried as front line treatment for patients with acquired FVIII inhibitors.