Congenital factor X deficiency (FXD) is an autosomal recessive bleeding disorder caused by mutations in the F10 gene with a prevalence of 1:1 000 000. 1 FXD is one of the most severe rare bleeding disorders, and the bleeding phenotype correlates well with plasma FX activity levels (FX:C). Patients with severe FXD often present in the neonatal period with umbilical stump bleeding or intracranial hemorrhage (ICH). Throughout life, these patients can experience hemarthroses, intramuscular hematomas, and gastrointestinal bleeding. Patients with moderate or mild FXD manifest mucocutaneous bleeding and excessive traumatic and postsurgical bleeding. 2-4 Long-term prophylaxis with infusions of FX-containing products is recommended in patients with FXD and a personal or family history of severe bleeding. 1,5-7 Until recently, fresh frozen plasma (FFP) or prothrombin complex concentrates (PCCs) were the primary source of FX infusions. Because of the