Blood in the urine (hematuria). While this is a common condition for people who have hemophilia, it usually is not dangerous when it is treated appropriately. Blood clots that form in the urethra can cause sharp pain in the lower part of the belly because urine flow out of the bladder is blocked.
Bleeding in the digestive system, most often noticed in vomit or in the stool. Blood in the digestive system may sometimes cause vomit that looks like coffee grounds or give a black and tarry appearance to the stool. If enough blood is lost, you might have symptoms of anemia, such as lightheadedness, weakness, and fatigue.
Bleeding inside the head (intracranial hemorrhage). Often a result of a head injury, this is very dangerous because it may cause brain damage and death.
Compartment syndrome, a rare complication that develops when bleeding in the muscle puts pressure on arteries and nerves inside the muscle. This syndrome can cause serious damage to the limb.