Background: The special interest group (SIG) on Translation and Cultural Adaptation (TCA) had its first meeting in Hong Kong at the 2004 Annual ISOQOL meeting. The overall objective of the TCA SIG is to identify and advance research in different areas of interest to all parties involved in the field of Translation and Cultural Adaptation. Three priority areas of research were identified and organised in three subgroups: translation difficulties, equivalences and methodologies. OBJECTIVES: The objectives of subgroup one are: 1. To collect, review and analyse examples of translations difficulties in the adaptation of Patient-Reported Outcomes (PRO) measures; 2. To create a list of "good practices" for developers of questionnaires and translators, based on the review of common translation difficulties and proposed solutions on how to prevent them. METHODS: The group has organised its activities in 4 steps: 1. Categorisation of difficulties; 2. Collection of examples of translation difficulties; 3. Review of examples; and 4. Recommendations. RESULTS: Translation difficulties were divided into categories according to: 1. Their position within the PRO questionnaire (i.e. Demographics, levels of education, "race", Instructions, Items and Response Choices); 2.The layout used, e.g. e-layout, tables, font-related problems; and 3. Their nature: Cultural (Is the construct to be measured relevant in the target cultures?); Conceptual and Semantic (Do the items represent the construct definition?); Syntactic; and Idiomatic. Examples of translation difficulties for each category defined previously and for a selection of families and branches of languages have been collected and will be presented. Recommendations on how to prevent potential translation difficulties will be proposed to developers of PRO questionnaires. CONCLUSION: The translation of PRO measures is a difficult task. "Good practices" for the development and translation of PRO measures should be implemented to facilitate the use of linguistically valid PRO measures in international research.