Severe haemophilia is associated with bleeding into joints and development of arthropathy. Prophylactic treatment with infusion of replacement clotting factor is known to prevent bleeding, preserve joint functioning and result in higher health-related quality of life (HRQoL) than episodic treatment; however, adhering to standard prophylaxis schedules can be difficult, and little is known about the relationship between adherence to prophylactic treatment and outcomes. The aim of this study was to assess the relationship between self-reported adherence to prophylaxis and health outcomes, including HRQoL and bleeding episodes. Adults with haemophilia (n = 55) and caregivers of children with haemophilia (n = 55) in Australia, Canada, and the United States completed an online questionnaire which included measures of HRQoL (SF-12v2 for adults and SF-10 for caregivers of children), self-reported bleeding episodes, and the VERITAS-Pro measure of adherence to prophylaxis in haemophilia. Regression analysis was used to test the association between VERITAS-Pro total score and outcomes. Poorer adherence (higher VERITAS-Pro scores) was associated with a greater number of self-reported bleeding episodes in the past year among adults (p < 0.01), more days of work/school missed among paediatric patients (p < 0.01), and lower physical health status scores among paediatric patients (p < 0.05). This study highlights the benefits of adherence to prophylaxis among those with severe haemophilia and provides evidence for the utility of the VERITAS-Pro by demonstrating a relationship between adherence and outcomes.