In LEOPOLD Kids Part B, BAY 81–8973 was found to be effective for the prevention and treatment of bleeds in PUPs and MTPs <6 years of age with severe hemophilia A. Consistent with the use of this class of FVIII product in PUPs/MTPs, inhibitor development was the most frequently reported AE, albeit occurring at a slightly higher frequency than has been reported by other studies of FVIII products in PUPs/MTPs. This evidence concerns the gene F8 and hemophilia A.