Patients with severe haemophilia are treated either in case of bleeds only (on demand), or with regular infusions of clotting factor to prevent bleeds (prophylaxis). The introduction of prophylaxis has been hampered by issues of cost and viral safety. In order to compare results and treatment cost of different treatment strategies in adults, three cohorts of patients with severe haemophilia (born 1970-1980) were compared. 106 French patients were treated on demand, 49 Dutch patients were treated with intermediate dose prophylaxis, and 24 Swedish patients were treated with high dose prophylaxis. The annual number of joint bleeds, and the radiological Pettersson score were used to compare outcome, annual clotting factor consumption was used to compare costs. Prophylaxis reduced bleeds and arthropathy: patients treated on demand had a median of 11.5 joint bleeds/year and a median Pettersson score of 16 points, for intermediate dose prophylaxis median bleeds were 2.8 and Pettersson score was 7 points, and for high dose prophylaxis median bleeds were 0.5 joint bleeds and Pettersson score was 4 points. All differences were statistically significant, except the Pettersson scores in both prophylactic regimens. Treatment cost was only increased for high dose prophylaxis: mean clotting factor consumption was 1612 IU kg-1 yr-1 for on demand treatment, 1488 IU kg-1 yr-1 for intermediate dose prophylaxis, and 4012 IU kg-1 yr-1 for high dose prophylaxis. In young adults, the cost of intermediate dose prophylaxis is similar, but outcome is better than for on demand treatment. The cost of high dose prophylaxis is twofold higher, further improving outcome only slightly.