Co-morbidities of haemophilia, such as arthropathy and blood-borne infections, can adversely affect the quality of life of adult patients with haemophilia. The purpose of this study was to develop and validate a haemophilia-specific health-related quality of life questionnaire for adults (HAEMO-QoL-A). Subjects with varying severities of haemophilia completed the HAEMO-QoL-A at baseline and 4 weeks. Other assessments included the SF-36 and Health Assessment Questionnaire - Functional Disability Index (HAQ-FDI). Two-hundred and twenty-one participants completed the 41-item HAEMO-QoL-A covering six domains (Physical Functioning, Role Functioning, Worry, Consequences of Bleeding, Emotional Impact and Treatment Concerns) and four independent items. Internal consistency was good-to-excellent (Cronbach's alpha-range: 0.75-0.95). Test-retest reproducibility was good, with intraclass correlation coefficients >0.80 except for the Emotional Impact domain (0.79). Concurrent validity between the HAEMO-QoL-A total and subscale scores and all SF-36 subscale scores were generally good (correlations range: 0.13-0.87). Significant correlations between the HAEMO-QoL-A and the HAQ-FDI ranged from -0.14 to -0.69. There were non-significant correlations with the Treatment Concerns subscale and with the Worry subscale. The HAEMO-QoL-A discriminated significantly between adults with haemophilia by severity and HIV status. The Physical Functioning subscale discriminated between patients receiving prophylactic or on-demand therapy. The HAEMO-QoL-A is a valid and reliable instrument for assessing quality of life in haemophilia patients.