Induction of factor VIII (FVIII) inhibitors sometimes occurs in patients with hemophilia due to frequent supplementation of FVIII. The inhibitor is rarely detected in non-hemophilic patients; however, an association has been described in patients with chronic inflammatory diseases, such as autoimmune diseases (e.g. SLE and rheumatoid arthritis), malignant tumors and drug allergies, and also to pregnant or aged individuals without underlying disease. We report on an 82-year-old patient who was transferred to our hospital after the diagnosis of acquired FVIII inhibitor. On admission the laboratory results showed no detectable FVIII activity (0%, normal range 70-100%), prolongation of coagulation time (APTT 102.4 s), and severe anemia 7.8 g/dL (normal range 12-16 g/dL). On physical examination multiple subcutaneous hematomas were detected and further bleeding in his left pectoralis muscle was observed. Despite extensive investigation no underlying disease was detected. Thirty-six courses of plasma exchange with 360 units of fresh frozen plasma replacement daily were conducted. High dose steroids and mycophenolate mofetil (MMF) were given throughout the course, and cyclophosphamide was administered once. Thirty-four units of erythrocytes were applied during this time. After 36 courses of plasma exchange in combination with high dose steroids, FVIII activity and coagulation time normalized and bleeding could be stopped. The patient was discharged in good health 48 days after admission. Hence, we present a case of severe idiopathic FVIII inhibitor-positive hemophilia successfully treated with the combination of plasma exchange, corticosteroids, cyclophosphamide and MMF.