Hemophilia B (Cairn terrier type) is an inherited bleeding disorder affecting dogs. Hemophilia B (Cairn terrier type) is caused by a deficiency of coagulation factor IX, an essential protein needed for normal blood clotting. There is variation between breeds in the severity of the bleeding tendency with this disease. More severely affected dogs bruise easily and often get blood filled masses (hematomas) under their skin and within muscles with mild trauma. They can also have internal bleeding and bloody or dark tarry feces. Dogs may show signs of lameness or stiffness if bleeding in the joints is present. A mildly affected dog may present with easy and excessive bruising and frequent nosebleeds. There is significant risk for prolonged bleeding after surgery or trauma, and in some cases, the bleeding may be severe enough to cause death. Veterinarians performing surgery on known affected dogs should have ready access to blood banked for transfusions. Most dogs will have a normal lifespan with this condition despite increased blood clotting times.