Haemophilia is a congenital bleeding disorder with a prevalence of 1:10,000 inhabitants. Treatment of patients with haemophilia requires a substantial amount of economical and human resources, why patient-rated outcomes (PROs) such as Quality of Life (QoL) and treatment satisfaction (TS) are considered increasingly more important in this field. For the adequate assessment of PROs cross-culturally validated disease-specific instruments are necessary. OBJECTIVES: Linguistic validation of 3 haemophilia-specific PROs for the assessment of TS (Hemo-Sat) and QoL, both in children (Haemo-QoL: 3 age group versions for children 4-7, 8-12, 13-16 years and their parents) and in adults (Haem-A-QoL) in up to 32 languages. METHODS: For languages where no translation existed, the process was conducted by a specialist in each target country using the following standardized methodology: (1) two forward translations by professional translators, native speakers of the target language and fluent in English; (2) comparison and reconciliation of the translations by the specialist in the target country; (3) backward translation by a native English speaker; (4) comparison of source and backward version; (5) review by the developer for a selection of languages; creation of the different forms of the instrument; (6) review by a clinician. RESULTS: The Haemo-QoL was linguistically validated into 32 languages, Haem-A-QoL (n=29) and Hemo-Sat (n=19). Besides the challenge of ensuring conceptual equivalence with the original and cultural appropriateness, the translation process revealed 2 additional difficulties. When translating an expression, appropriate terms had to be found for each age group whilst maintaining consistency across all versions of the same language. CONCLUSIONS: The language versions of Haemo-QoL, Haem-A-QoL and Hemo-Sat were established according to a rigorous translation methodology aiming to ensure conceptual equivalence across different language versions facilitating international comparison and pooling of data. The linguistic validation process is necessary before using PROs in international trials.