Severe haemophilia (factor [F]VIII/FIX activity < 0.01 IU mL(-1)) is characterized by repeated haemarthroses resulting in severe arthropathy in adulthood. In 1958, Professor Nilsson in Sweden introduced prophylactic infusions with clotting factor concentrates at regular intervals in order to maintain clotting factor levels above 0.01 IU mL(-1) and to prevent bleeding. Since then, evidence of the long-term beneficial effects of prophylactic treatment for severe haemophilia has been increasing and it has become the recommended treatment strategy for children with severe haemophilia by both the World Health Organization and the US National Hemophilia Foundation Medical and Scientific Advisory Committee. However, the implementation of this recommendation has been hampered by issues of cost and venous access. The high costs of prophylaxis have largely prevented its use in major parts of the world. The question therefore is whether the current models of replacement of clotting factor concentrates, while certainly being effective, are also optimal. Can the data on outcome at different levels of factor replacement be used to assess their cost-effectiveness?