OBJECTIVES: Prior to use in an international study, the Hospital Anxiety and Depression Scale (HADS) underwent linguistic validation in 30 languages. The original scale was developed in UK English to detect states of anxiety and depression in and outside hospital and also community settings. A rigorous methodology was required to ensure conceptual equivalence and cultural relevance across different languages. METHODS: The translation process was conducted by a specialist in each target country using the following standardized methodology: 1) two forward translations by professional translators who were 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; and 5) review by the developer. The linguistic validation methodology for some languages deviated slightly from what is described above, as a translation already existed; the translation process started at the backward translation step on the existing version. RESULTS: The translation process revealed linguistic and conceptual challenges. Translating idiomatic expressions often required paraphrasing to convey the intended meaning whenever a literal equivalent was not conceptually equivalent and culturally relevant. In addition, while in most language versions it was possible to retain the same tense as in the original instrument without alteration of meaning, in a few translations it proved necessary to use a different tense to achieve clarity and equivalence of concept. CONCLUSION: The language versions of the HADS were established according to a rigorous translation methodology. The process aims 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.