The aim of this study was to develop and validate an index to assess the implementation of quality management systems (QMSs) in European countries.Questionnaire development was facilitated through expert opinion, literature review and earlier empirical research. A cross-sectional online survey utilizing the questionnaire was undertaken between May 2011 and February 2012. We used psychometric methods to explore the factor structure, reliability and validity of the instrument.As part of the Deepening our Understanding of Quality improvement in Europe (DUQuE) project, we invited a random sample of 188 hospitals in 7 countries. The quality managers of these hospitals were the main respondents.The extent of implementation of QMSs.Factor analysis yielded nine scales, which were combined to build the Quality Management Systems Index. Cronbach's reliability coefficients were satisfactory (ranging from 0.72 to 0.82) for eight scales and low for one scale (0.48). Corrected item-total correlations provided adequate evidence of factor homogeneity. Inter-scale correlations showed that every factor was related, but also distinct, and added to the index. Construct validity testing showed that the index was related to recent measures of quality. Participating hospitals attained a mean value of 19.7 (standard deviation of 4.7) on the index that theoretically ranged from 0 to 27.Assessing QMSs across Europe has the potential to help policy-makers and other stakeholders to compare hospitals and focus on the most important areas for improvement.