OBJECTIVES: To harmonize VAS values resulting from 11 studies in 6 countries (England, Finland, Germany, The Netherlands, Spain and Sweden) using the EQ-5D valuation questionnaire, developed by the EuroQol Group. The aim is to make available a European EQ-5D value set and to gain insight into the influences resulting from the prevailing differences in methodology and sample characteristics. METHODS: The database constructed for this research project contains data on more than 110.000 health states from 8370 respondents. Appropriate transformation was applied to deal with ceiling and floor effects. Regression models and a single value decomposition were applied to explore the differences between the valuations in the 11 samples and the influences of background variables on the VAS values of a subset of 18 health states. Multilevel regression analysis on data of 49 health states was conducted to take into account characteristics at the individual respondent level while testing the impact of health state characteristics on the value set. RESULTS: In general, the impact of the background variables such as age and experience of illness on the VAS valuations appeared to be modest. Differences in study methodology have a higher impact on the VAS values but differences in the health states themselves were found to be the major determinant of VAS values. CONCLUSIONS: When corrected for the influence of the background variables, the VAS values from the 6 countries showed a remarkable agreement. Differences can be attributed to differences in survey methodology and sample characteristics rather than 'cultural' aspects. By using a simple instrument, ie., the EQ-5D valuation questionnaire, it seems that an internationally consistent EQ-5D value set can be established.