Hemophilia A is a genetic deficiency of factor VIII that causes blood to clot too slowly. The disease is classified based on how much factor VIII is in the blood. People with mild or moderate hemophilia A have low, but detectable, blood levels of factor VIII and bleed with trauma or surgery. At the time of surgery, they need to receive factor VIII replacement by infusion into the vein so that blood can clot normally and abnormal bleeding can be avoided. A complication of hemophilia A is the development of an antibody that binds factor VIII and makes the factor VIII infused for treatment not work properly. This antibody is called an inhibitor. In mild and moderate hemophilia A, inhibitors are not common, but have been reported to occur after intensive factor VIII infusions, as may occur at the time of surgery. This study is designed to observe people with mild and moderate hemophilia A who are having surgery. Information on the surgery, treatments given, bleeding, and infection will be gathered. Also, blood will be drawn to determine how the immune system is reacting to the factor VIII. No specific treatments will be given as part of this study. We will use the information to determine what influences inhibitor development. A better understanding of inhibitor development will help medical providers do things to avoid inhibitor development in this population or researchers to design new treatments.