Introduction: Assessment of the performance of management systems is one of the main concerns of managers. The measure of success of an occupational health and safety management system is the ex-tent of its effectiveness. The effects of implementing an OHSMS on health and safety perfor-mance indices in a casting site located in Iran between 2015 and 2019 were examined. Methods: A retrospective descriptive-analytical study was conducted over five years on 21 depart-ments of a casting site. All the functional indices one year before the implementation of OHSAS 18001:2007 in 2015 until a year after the implementation (2019) were monitored and the data were analyzed using SPSS (v.19). Results: There was a significant decrease in occupational accidents after the implementation of OHSAS 18001:2007. Mechanical and ergonomic factors demonstrated significant improvements. There were improvements in the indices of opening health files for the personnel, personal protective equipment, education, instructions, legal requirements, commitment, and leadership. There was no significant change in chemical and physical factors. Conclusion: Implementation of the occupational health and safety manage-ment system was effective in the indices that needed managerial control with no or low expenses. However, it was not effective in indices in engineering and technical areas that needed more expenses.