Prophylaxis is standard of care for boys with severe haemophilia A. Indications for prophylaxis in adulthood, non-severe haemophilia A, haemophilia B and haemophilia with inhibitors are less well defined. This survey, conducted in 2006, aimed to describe prophylaxis use in patients of all ages and severities with haemophilia A or haemophilia B in Canada. Data on 2663 individuals (2161 haemophilia A; 502 haemophilia B), including 78 inhibitor-positive patients, were returned by 22/25 Canadian haemophilia treatment centres. This represented 98% of the Canadian haemophilia population. Frequency of prophylaxis use, defined as infusion of factor VIII/IX concentrate at least once weekly for >/=45 weeks of the year, was highest in individuals with severe haemophilia A (69%). It was lower in individuals with severe haemophilia B (32%), moderate haemophilia A (18%) or B (5%) and mild haemophilia A (1%) or B (1%). Among individuals with severe haemophilia A, the frequency of prophylaxis use was 84% in children (</=18 years) and 55% in adults (>18 years). Thirteen per cent of inhibitor-positive individuals were receiving prophylaxis with bypassing agents. Comparison with data obtained from a 2002 Canadian survey showed a greater use of prophylaxis in children </=5 years of age with severe haemophilia A (73% vs. 49%). Prophylaxis is no longer confined to children with severe haemophilia A, but is used in a significant proportion of adults with severe haemophilia A and individuals with severe haemophilia B or moderate haemophilia A. Prophylaxis is being started earlier in boys with severe haemophilia A.