Objective To analyze a case of violations by an occupational medical examination (OME) institution and to explore the key control points for the supervision and management of OME institutions, as well as the core role of quality assessment in this context. Methods An OME institution suspected of illegal activities was used as the study subject. Retrospective analysis was conducted. Clues of suspected violations were identified by an on-site quality assessment. After investigation and verification by the local health authorities, legal action was taken against the institution for its violations. Results During an on-site quality assessment, the Guangdong Province OME quality control expert group discovered that the OME institution violated regulations, including unqualified personnel file, exceeding the scope of services category, issuing false reports, failing to report suspected occupational diseases on time, and failing to notify workers about suspected occupational diseases as required. The evidence was then submitted to the Guangdong Province OME Quality Control Center, which subsequently forwarded the case to local health administration department for filing and investigation. After the investigation, penalties were imposed on the OME institution for its illegal activities. Conclusion The key supervision and inspection points in the quality assessment of OME institutions include personnel file configuration, the quality control management system and its implementation, the quality of OME reports, and information reporting. Quality assessment plays a pivotal role in ensuring the legal and compliant practice of OME institutions, safeguarding the health rights and interests of workers, and enhancing the overall standard of the OME industry.