INTRODUCTION: The increase of patient-based assessments in clinical trials has emphasized the need for cross-culturally valid instruments to pool data across countries. The Work Limitations Questionnaire (WLQ) consists of 25 questions divided into 4 scales, was developed in US English and is designed for the assessment of the impact of health problems on work. METHODS: Prior to use in an international trial, the original questionnaire underwent linguistic validation in 3 languages. Coordinated by a QoL specialist in each target country, an internationally recognised translation methodology was followed: preliminary versions in Canadian French and US Spanish were established after forward/backward translation. The Canadian English version was established after a review of the original by a QoL specialist in Canada. Throughout the process the author clarified the concepts underlying each item. RESULTS: Linguistic and conceptual issues arose during the translation process. The notion of "work without stopping to take breaks or rests" could not be translated literally, as in some countries, it is illegal not to take breaks. It was therefore translated as "work without stopping to take more breaks than usual". Likewise, the alternative use of "clients" and "customers" in the original could be translated by only one word in the translations. CONCLUSION: The steps performed ensure the conceptual equivalence between the original and the preliminary language versions. Testing on a sample target population in each country and the comparison of all languages will ensure the clarity, appropriateness of wording and acceptability of the translations as well as their international harmonization. Psychometric testing will be important to ensure similar relationships among scales across countries.