Psychosocial factors at work have been found to be associated with having potential risk for adverse health effects. The main instrument used to measure these factors and their impact is the Job Content Questionnaire (JCQ) by Karasek. The objective of this study was to evaluate the psychometric properties of the French version of the JCQ, and in particular to assess its internal coherence and consistency, as well as the factorial and convergent validity of psychological demands, decisional latitude and social support at work based upon the SUMER survey, which was the first French national survey of its kind to include the JCQ. The study was based on a sample of 24, 486 workers who answered the JCQ in 2003 (96.5% response rate). Internal consistency was satisfactory, as Cronbach's alpha coefficients were observed as being higher than 0.65. Confirmatory factor analysis showed that the best model was composed of 5 latent variables: demands and pressures, the two dimensions of latitude (utilization of skills and autonomous decision-making), and the two dimensions of support (from supervisors and from colleagues). Convergent validity tests confirmed the expected association with key variables, which were: age, work status, sector of activity, occupation, job satisfaction, perception of job stress, and intent to change job. This study demonstrated satisfactory psychometric properties of Karasek's JCQ scales for the French working population.