OBJECTIVE: The increasing inclusion of Patient Reported Outcome (PRO) measures in large multi-country trials has introduced many new methodological challenges. PROs are often developed in English and translated into the various languages needed to support these global trials. Data is often pooled and there are concerns about the process, but currently no established criteria, to assure the appropriateness of the aggregation of data derived from multiple languages and cultures. METHODS: A literature review was conducted in order to investigate what methods have been used to assess measurement equivalence across translated PROs. Discussions were held between members of the task force and comments were sought from the ISPOR membership. RESULTS: A diverse range of methods have been employed to assess measurement equivalence across translated PROs. These include: classical test theory, factor analysis, structural equation modelling (SEM), and Differential Item Functioning (DIF). Basic measurement characteristics such as means, standard deviations etc have been evaluated when the samples are large enough, or basic measurement properties (distribution, internal consistency etc) have been verified in a at least a few languages. If measurement equivalence is lacking it is suggested that qualitative research, analysis of existing trial datasets, and/or consultation with in-country health professionals could be carried out to investigate possible reasons for the lack of equivalence. CONCLUSION: While data pooling across languages/cultures is common practice, there is no clear recommendation about methods  or the level of measurement equivalence required to determine whether pooling is appropriate or not. There is a need for practical steps to be taken in order to investigate and resolve lack of measurement equivalence and a great need for further research in this area.