Objective: Prior to use in an international study collecting data from haemophiliacs, the Haemo-QoL and Haem-A-QoL underwent linguistic validation in 17 languages. Whilst the original Haemo-QoL was developed in British English, the Haem-A-QoL had been developed in Italian. For the purposes of linguistic validation, an English version of the latter was used as a basis for the translations. Seven distinct versions exist: an adult form (Haem-A-QoL) and child self-report and parent proxy versions (Haemo-QoL) for 3 distinct age groups (4-7, 8-12, 13-16 years). A rigorous methodology was required to ensure conceptual equivalence and cultural relevance across different 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; and 6) review by a clinician. Existing translations were integrated into the process as appropriate. Results: Besides the challenge of ensuring conceptual equivalence with the original and cultural appropriateness, the translation process revealed two 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. Conclusion: The language versions of Haemo-QoL and Haem-A-QoL were established according to a rigorous translation methodology aiming to ensure conceptual equivalence across different language versions to facilitate international comparison and pooling of data. The linguistic validation process as a whole supports the advantage of integrating international feedback on concepts and wording before a questionnaire is finalized.