BACKGROUND: Most epidemiological data concerning low back pain (LBP) are from high-income countries and there is very little information about LBP in the working population in developing countries. OBJECTIVES: To determine the prevalence of LBP in Iranian industrial workers. To explore associations between LBP and physical and psychosocial factors at work, as well as lifestyle factors. METHODS: Cross-sectional study of the largest car-manufacturing group in Iran. The prevalence of LBP, work exposures and lifestyle factors were recorded using the standardized Nordic questionnaire for analysis of musculoskeletal symptoms. Demographic data and lifestyle factors (age, sex, education, weight, work experience, smoking and fitness training) were also collected. RESULTS: Of the 18,031 employees, 78% participated. The majority of subjects in this study population were young males (