Hemophilia is not one disease but rather one of a group of inherited bleeding disorders that cause abnormal or exaggerated bleeding and poor blood clotting. The term is most commonly used to refer to two specific conditions known as hemophilia A and hemophilia B, which will be the main subjects of this article. Hemophilia A and B are distinguished by the specific gene that is mutated (altered to become defective) and codes for a defective clotting factor (protein) in each disease. Rarely, hemophilia C is encountered, but its effect on clotting is far less pronounced than A or B.

Signs and symptoms of spontaneous bleeding include:
1. Pain, swelling or tightness in your joints
2. Blood in your urine or stool
3. Nosebleeds without a known cause
4. Unexplained and excessive bleeding from cuts or injuries, or after surgery or dental work
5. Many large or deep bruises
6. Unusual bleeding after vaccinations
7. In infants, unexplained irritability

Emergency signs and symptoms of hemophilia include:
1. Sudden pain, swelling and warmth in large joints, such as knees, elbows, hips and shoulders, arm and leg muscles
2. Bleeding from an injury, especially if you have a severe form of hemophilia
3. Painful, prolonged headache
4. Repeated vomiting
5. Extreme fatigue
6. Neck pain
7. Double vision