There has been an ongoing debate as to whether hemophilia A (HA) is more severe than hemophilia B (HB), and there are studies supporting each side of the argument. The study aimed to investigate whether any differences in major bleeding events exist between patients with severe HA and HB. A nationwide, population-based retrospective cohort study using the National Health Insurance Research Database was conducted. We compared 658 patients with severe HA and 137 patients with severe HB without inhibitors from 1997 to 2013, during the period when adult patients older than 18 years old were treated with the on-demand therapy since birth. There was no significant difference between patients with severe HA and HB in the rate of major bleeding events, with an adjusted relative ratio of 0.79 (95% confidence interval. There was also no significant difference in the incidence rate of major bleeding events between adult patients with HA and HB with the on-demand therapy, and an adjusted hazard ratio (HR) of 0.82. However, patients with HA had a lower incidence rate of intracranial hemorrhage, with an adjusted HR of 0.44. In addition, no significant difference in the frequency of major bleeding events requiring hospitalization between patients with HA and HB was found, P > .05. In conclusion, the study demonstrated that patients with severe HB encountered a similar rate of major bleeding events to those with severe HA. For more information click here.