Background: Work-related musculoskeletal disorders (WMSDs) are a common health problem throughout the world and a major cause of disability in the workplace.

Objective: To determine the prevalence rate of MSDs, assessment of ergonomics working conditions and identification of major risk factors associated with MSDs symptoms among employees of Iranian petrochemical industries between October 2009 and December 2012.

Methods: In this study, we studied 1184 randomly selected employees of 4 Iranian petrochemical companies with at least one year of work experience in office or operational units. For those with office jobs, data were collected using Nordic Musculoskeletal disorders Questionnaire (NMQ) and ergonomics checklist for the assessment of working conditions. For those with operational jobs, NMQ and Quick Exposure Check (QEC) method were used for data collection.

Results: The most prevalent MSD symptoms were reported in lower back (41.5%) and neck (36.5%). The prevalence of MSDs in all body regions but elbows and thighs of the office staff was significantly higher than that of operational workers. Assessment of working conditions in office staff revealed that the lowest index was attributed to workstation. QEC technique among operational workers showed that in 73.8% of the workers studied, the level of exposure to musculoskeletal risks was "high" or "very high." MSDs were associated with type of job, age, body mass index, work experience, gender, marital status, educational level and type of employment.

Conclusion: The prevalence of MSDs in the office staff was higher than that of operational workers. Level of exposure to MSDs risk was high in operational workers. Corrective measures are thus necessary for improving working conditions for both office and operational units.