Background: This study aims to build a measure for assessing and reviewing the living conditions, care and human rights of people with longer term mental health problems in psychiatric and social care institutions. Protection of their human rights is imperative since impaired mental capacity secondary to mental illness can make them vulnerable to abuse and exploitation from others. They also constitute a major resource pressure for mental health services, social services, informal carers and society as a whole. Methods/Design: domains are identified by collating results from: i) a systematic review of the literature on institutional care for this service user group; ii) a review of the relevant care standards in each participating country; iii) Delphi exercises in partner countries with mental health professionals, service users, carers and advocates. Common domains and cross-cutting themes are agreed by the principal researchers and an international expert panel. Items are developed to assess these domains and incorporated into the toolkit which is designed to be administered through a face to face interview with the institution's manager. The toolkit is refined in response to inter-rater reliability testing, feedback from interviewers and interviewees regarding its utility, and feedback from key stakeholders in each country about its ability to deliver information that can be used within each country's established systems for quality assessment and review. Cross-validation of the toolkit ratings against service users' quality of life, autonomy and markers of recovery tests whether it can deliver a proxy-measure of the service users' experiences of care and the institution's promotion of their human rights and recovery. The ability of the toolkit to assess the "value for money" delivered by institutions is investigated by comparing toolkit ratings and service costs. The study will deliver the first international tool for the assessment of the quality of institutional care for people with longer term mental health problems that is accurate, reliable, informative, useful and easy to use.