Factor XIII (FXIII) deficiency is a very rare form of haemophilia resulting in different manifestations of bleeding disorders, but characterised by umbilical stump bleeding in up to 80% of patients. Although originally described as the final enzyme in the clotting cascade, FXIII is now recognised to play a role throughout the clotting process. Treatment with FXIII concentrate (Fibrogammin P, ZLB Behring) results in the re-establishment of a normal clotting pattern. Prophylaxis studies in France and the USA have demonstrated an excellent response following monthly prophylaxis with this plasma-derived, pasteurised concentrate. Patients with FXIII deficiency have good control of bleeding, with no development of inhibitors, or viral seroconversion. The development of registries such as that in the USA will enable the different manifestations of the disease to be explored.