BACKGROUND: Occupational health and safety (OHS) self-auditing is a common practice in industrial workplaces. However, few audit instruments have been tested for inter-rater reliability and accuracy. METHODS: A lockout/tagout (LOTO) self-audit checklist was developed for use in manufacturing enterprises. It was tested for inter-rater reliability and accuracy using responses of business self-auditors and external auditors. RESULTS: Inter-rater reliability at ten businesses was excellent (kappa = 0.84). Business self-auditors had high (100%) accuracy in identifying elements of LOTO practice that were present as well those that were absent (81% accuracy). Reliability and accuracy increased further when problematic checklist questions were removed from the analysis. CONCLUSIONS: Results indicate that the LOTO self-audit checklist would be useful in manufacturing firms' efforts to assess and improve their LOTO programs. In addition, a reliable self-audit instrument removes the need for external auditors to visit worksites, thereby expanding capacity for outreach and intervention while minimizing costs.