If you have hemophilia, you have little or no clotting factor. Clotting factor is a protein needed for normal blood clotting. Without it, you may bleed for a long time after an injury or accident. You also may bleed into your knees, ankles, and elbows. Bleeding in the joints causes pain and, if not treated, can lead to arthritis. Bleeding in the brain, a very serious complication of hemophilia, requires emergency treatment.