The case of a 72 year-old man with a sinus histiocytosis is reported. The clinical course was characterised by an hemorrhagic disorder linked to a factor VIII inhibitor. The characteristics of the antibody titer, affinity and saturability have been studied. In an attempt to stop the bleeding treatment included human and porcine factor VIII concentrates, plasmapheresis and immunosuppressive drugs. Repeated plasma exchanges did not modify the inhibitor titer for more than 24 h.