Most of the physical, psychosocial and financial disability in severe haemophilia A is caused by the effects of recurrent haemarthroses and of chronic arthritis. Recent evidence suggests that this morbidity is related to insufficient factor VIII replacement therapy, not only quantitative (annual dose) but also qualitative (need for regular long-term prophylaxis). The recent development of recombinant factor VIII may increase the acceptability of prophylaxis to parents and patients, and hence reduce morbid outcomes.