To review long-term prophylactic factor treatment in young patients with severe haemophilia A and B, focusing on the orthopaedic and radiological outcome. We received 34 patients with severe haemophilia A (n = 29) and B (n = 5), aged 7-22 years. Age at start of treatment was 1-4.5 years. Dosages of factor concentrate (F VIII and F IX, respectively) were 25-40 IU/kg body weight, three times a week for haemophilia A and twice a week for haemophilia B. The patients had been checked annually over a 5-year period (1990-95). Orthopaedic and radiological joint scores were evaluated according to recommendations by the World Federation of Haemophilia. All results were obtained at the Department for Coagulation Disorders, University of Lund, Malmö University Hospital, Malmö, Sweden. Orthopaedic and radiological joint scores were found to have remained unchanged during follow-up in almost all patients and to be still zero (i.e. no unaffected joints) in 79% (n = 27) of the patients. There is a growing international consensus haemophilic arthropathy can be prevented by administering early high-dose prophylaxis. The results of the present investigation strongly support this opinion.