OBJECTIVES: To evaluate the cross-cultural equivalence of PRO measures and their translations the IQOD programme - the international Health-Related QoL Outcomes Database - selected three questionnaires. Although classical psychometric methods used for the evaluation of the Psychological General Well-Being Index (PGWBI) reflect systematic replications of results across the 17 translations, tests of differential item functioning (DIF) for mental health as latent variable failed for several languages and item response theory (IRT) tests for all languages. A reason for this is the co-existence of 20 different 6-point response categories investigating frequency and intensity for the 22-item questionnaire making mistranslations and the introduction of confounding constructs possible. A revision of the original formulations in terms of an analysis of their translatability before the creation of language versions could have avoided this issue. METHODS: A translatability assessment can be defined as an international critical review of a pre-final original in collaboration with the developer. In the absence of international development, this may be a cost- and time-effective alternative to the WHO approach to instrument design. As the translation process reveals difficulties when adapting concepts, idiomatic expressions, response scales, format, instructions and demographic items, these aspects are reviewed and items re-formulated taking the constraints of other cultures into account. RESULTS: Several examples of the impact of translatability assessment on the PGWBI will be given. Most importantly, had the process been conducted prior to translation and testing the 14 response scales investigating intensity could have been reduced to 1 and the 2 response scales investigating frequency could have also been reduced to 1. The total number of response scales could have been reduced from 20 to 3, thus facilitating translations and ultimately DIF and IRT tests results. CONCLUSION: Translatability assessment may be a practical way to incorporate international input into instrument development, thereby facilitating subsequent translation and ultimately the coherence of international data.