OBJECTIVE: An epidemiological surveillance system of work-related musculoskeletal disorders of the upper limb (MSDs) was implemented in 2002 in the Pays de la Loire region to assess the prevalence of the MSDs and their biomechanical and psychosocial risk factors in the working population. We will report here only the results concerning the exposure to psychosocial stress in the work environment. According to the Karasek "demand-autonomy" model, high psychological work demands may increase risk of ill health, particularly if there is a low level of decision latitude for the employees and low social support by the hierarchy or colleagues. METHODS: In 2002, 68 out a total of 400 occupational physicians volunteered to participate in the surveillance program and included 1 495 workers (895 men, 600 women) representative of the region's workforce. Work history and work environment were assessed by a self-administered questionnaire before the compulsory annual visit of occupational physicians. Exposure to psychosocial stress at work was assessed with the Job Content Questionnaire (JCQ) developed by Karasek. The three scales of decision latitude, social support and psychological demands were calculated using Karasek's recommendations. RESULTS: The mean scores of psychological demands, decision latitude and social support were 69.3 +/- 12.7; 22.3 +/- 3.2; 24.0 +/- 3.5, respectively. No differences were observed according to gender and age. A third of the workers were exposed to high psychological demands at work and most of them (61%) had little decision latitude to cope with work constraints. About 28% of workers suffered from a lack of social support from their colleagues or supervisors. Overall, about 17% of workers were exposed to a situation of "Job strain" (ie a combination of a high level of psychological demands and a low level of decision latitude) and 7% were exposed to a situation of "Job strain" with social isolation ("Job strain" with low social support). The situations of "Job strain", associated or not with a low level of social support, were particularly frequent in industries with taylorized work organisation, like the food industry and automobile industry, and in services characterised by strong merchant constrains, such as trade and cleaning services, for example. The frequency of "Job strain", with or without social isolation, was almost double in temporary workers. DISCUSSION: This study confirms that in a representative sample of workers, the exposure to occupational stress is not limited to managers and professionals, but concerns also a large number of employees and blue-collar workers of the public and private sectors. In general, the strongly qualified occupations are characterised by a high level of psychological demands, but individuals have large decision latitude to cope, which allows them to develop their capacities. The less qualified occupations are generally less confronted with a high level of mental demands than the managers and professionals. However, these individuals do not have enough decision latitude to cope with psychological demands which could lead to a high level of "Job strain", notably in the case of lack of social support from the supervisors and the colleagues. CONCLUSION: The study shows that the exposure to occupational stress is not limited to managers and professionals, but also concerns numerous employees and blue-collar workers. The determinants of work strain differ depending on occupations and this should be taken into consideration when implementing prevention programs for stress at work.