Prophylaxis for haemophilia improves outcomes, but at a substantial cost. Cost-utility analysis balances improvements seen in health-related quality of life (HRQoL) against costs, with the purpose of aiding healthcare decision-making. This analysis uses a measure of HRQoL known as utility. The objective of this study was to measure HRQoL (utility) values for states of health that result from on-demand therapy or prophylaxis. The HRQoL for different health states (including target joint bleeding, different intensities of prophylaxis, and indwelling intravenous catheters [ports]) was measured for healthy adults (n=30), parents of haemophilic children (n=30), and adults with haemophilia (n=28). Parents and patients rated health states similarly. Healthy adults gave the lowest ratings. The following rank, in order of HRQoL, was obtained: prophylaxis (low > medium > high) > on-demand therapy > prophylaxis with port> prophylaxis with infected port > on-demand therapy with development of a target joint. We conclude that: (1) haemophilia and its treatment reduce HRQoL; (2) prophylaxis is preferred to on-demand therapy; (3) intravenous ports substantially reduce HRQoL; (4) and an intravenous port to provide prophylaxis is preferable to on-demand therapy if a target joint develops.