ObjectiveTools generally used in measuring patient safety incidents in general healthcare settings are not considered suitable for mental health settings. The aim of this study was to develop and evaluate a specialized trigger tool for mental health settings that could detect both traditionally defined adverse events (AEs) and other mental health–related patient safety incidents (MHPSIs).MethodsWe first defined and categorized AEs and MHPSIs based on existing literature and then developed a trigger list, initially consisting of 50 items, which was subsequently reduced to 25 items after a pilot study. We then explored the properties of this final 25-item trigger tool, the Mental Health Trigger Tool (MHTT), through a retrospective review of 515 patient records with a two-stage review process similar to Global Trigger Tool methodology. We used findings of an alternative method of review which consisted of page-to-page reviews of patient records in the analysis of properties of MHTT.ResultsUsing the MHTT, at least one AE was identified in 98 patient records (19%) and at least one MHPSI was identified in 58 patient records (11%). The MHTT had a sensitivity of 98.6% and its specificity was 100%. The probability of finding an AE/MHPSI when any trigger was detected in a patient record with MHTT was 33.8% and that of individual triggers ranged from 0% to 100%.ConclusionsThe MHTT may offer an effective, practical, and easy-to-use method in identifying and measuring safety incidents in mental health settings.