For persons with mental illness and addictions, comprehensive assessment of their strengths, preferences and needs is central to person-centred care planning. In this study, the validity of the Mental Health Assessment Protocols (MHAPs) embedded in the Resident Assessment Instrument Mental Health instrument (the mandated assessment system for Ontario adult inpatient psychiatry) is examined, and triggering rates are compared in inpatient and community-based mental health settings. The sample is based on adults admitted to a psychiatric facility (n = 963) and to community mental health programmes (n = 1505) participating in the study. An international panel of mental health experts further evaluated study results. Among the 27 MHAPs, all but one had sensitivity rates above 80%, and the specificity was over 80% for 74% of the MHAPs. The expert panel found that the MHAPs worked well and could be used to support mental health care. The present study found that the MHAPs are valid measures, though more complex triggering algorithms capable of differentiating individuals based on outcomes were suggested to enhance their clinical relevance to care planning. Further, the use of compatible instrumentation in community-based mental health settings was promoted to enhance continuity of care.