The incidence of inhibitors among people with severe hemophilia A has been documented as approximately 20-30% in several prospective studies. In such patients acute hemorrhages frequently occur and profoundly jeopardize health, with subsequent development of arthropathy. A common way of treating such bleeding episodes is to use bypassing agents. Among these agents the prothrombin complex concentrate FEIBA has been widely used for many years. More recently, recombinant factor VIIa (NovoSeven) has been added to the therapeutic options. While both products have been found effective in treating hemorrhages, the number of injections given for a bleeding episode has ranged widely, and it is so far unknown whether one of the products might have a better effect in certain patients.