Our research group on paediatric haematology is focused on bleeding- and coagulation disorders in children, in particular on haemophilia and venous thrombosis. Haemophilia A and B are hereditary, X chromosomal recessive bleeding disorders caused by deficiency or absence of coagulation factors VIII (FVIII) or IX (FIX) in the blood. The general aim of this part of the research program is to improve our knowledge of the F8 and F9 genes and use it for carrier- and prenatal diagnosis and in prediction of risk development of inhibitors to treatment with FVIII/IX which is the most important clinical problem in haemophilia today. In addition, we study environmental and therapy related risk factors for development of inhibitors to FVIII/IX, the epidemiology of haemophilia in Sweden and outcome measurers of treatment such as MRI of joint disease and the impact of prophylactic treatment on the frequency of intracranial hemorrhage.