An 88 year-old man was hospitalized because of bullous pemphigoid of the skin with detectable autoantibodies against type XVII collagen. During his stay in the hospital, he developed easily bleeding hemorrhagic bullous lesions of the oral mucosa, which were thought to be an oral manifestation of bullous pemphigoid. A thorough blood examination showed acquired haemophilia A, related to the development of autoantibodies against factor VIII.