Mental health problems have recently increased among Japan Overseas Cooperation volunteers since 1965, when the Ministry of Foreign Affairs (Japan International Cooperation Agency) launched this volunteer work project for improving hygiene and socioeconomic conditions in developing countries. There was little research on job stress among them dispatched despite previous surveys indicating job as an important stressor. To investigate stress and job-related stressors among them, we conducted a cross-sectional epidemiological study from October to December in 2003. The subjects were all 1,084 Japan Overseas Cooperation volunteers aged 20-40, who worked in 67 countries worldwide at the time of this study (485 and 599 males and females, 316, 332 and 436 for those staying overseas for 11, 7 and 4 months, respectively). Approximately 80% were involved in their dispatching occupational organizations as professionals in information technology, health & welfare, education, and research. Our main outcome measure used was the Brief Job Stress Questionnaire, which was developed to assess stress and job-related stressors or buffers for Japanese workers. Demographic and personality (Egogram) characteristics as well as other health information were obtained. The response rate was 86.9%. For psychological stress, prevalence was 5.5% (n = 49). Means (+/- SD) were 4.22 (+/- 3.98), and 4.89 (+/- 4.40) for males and females (p < 0.05), and 5.15 (+/- 4.17), 5.05 (+/- 4.45), 3.93 (+/- 4.40) for those staying overseas for 11, 7 and 4 months (p < 0.01), respectively. For physical stress, prevalence was 2.9% (n = 26). Means (+/- SD) were 1.10 (+/- 1.68), and 1.41 (+/- 1.74) for males and females (p < 0.01), and 1.47 (+/- 1.77), 1.35 (+/- 1.89), 1.11 (+/- 1.55) for those staying overseas for 11, 7 and 4 months (p < 0.05), respectively. The factors significantly associated with psychological stress were high job demand, poor human relationships at work, low job suitability, low social support from supervisors and colleagues, and being dissatisfied with their life, according to multiple logistic regression analysis. The present study suggested that psychological stress was more prevalent than physical. It also implied a significant relationship between psychological stress and job-related stressors among the subjects of this study as in employees in Japan. Mental health check-ups and counseling in the early stage of psychological stress is important from the viewpoint of prevention of developing stress-related mental health disorders. Education on stress-coping skills should be considered in a training program before they are sent overseas.