Abstract Introduction : Treatment credibility and patient expectancy of improvement have been increasingly considered in clinical research. Objectives : The objective of this study was to carry out the cross-cultural validation of a French-language version of the credibility/expectancy questionnaire (CEQ), to further document the psychometric properties of the CEQ, and to add to the empirical data concerning the concepts of credibility and expectancy. Methods : The process followed up-to-date guidelines for cross-cultural adaptation and included extensive psychometric validation. Accurate translation and cross-cultural equivalence of the questionnaire's basic concepts were assessed by a multidisciplinary expert committee. Reliability and validity were evaluated in a cohort of 209 consecutive patients referred to health psychologists for psychotherapy for posttraumatic stress disorder. Results : The French CEQ was found to be well understood and acceptable. It demonstrated excellent reproducibility, consistency and factorial validity, confirming the 2-factor model separating credibility from expectancy of the original CEQ. The use of modern measurement methods indicated that the CEQ scales satisfy the important characteristics of unidimensionality and invariance across age and gender. Conclusion : The French CEQ can be used for French-speaking populations in various studies to evaluate both credibility and expectancy for improvement. However, the questionnaire's sensitivity to change should be further confirmed before it can be safely used in longitudinal studies. The study also confirms the close relation between credibility and expectancy but substantiates differences large enough to justify separate measurement of the two components of the questionnaire.