Mental health research and practice is currently moving beyond a focus on group-level symptom reduction models. Hence, research and treatment increasingly emphasize the real-life individual needs of service users and their social networks. One example is the Open Dialogue approach (OD), which has demonstrated promising outcomes in the Finnish Western Lapland (WL) catchment area. Nevertheless, it is unclear how OD-based services have so far been maintained in WL. It is also unclear how the experiences of multi-disciplinary care teams, service users and their social network members differ, with regard to differing approaches to mental health treatment. More generally, there is a global need for information on factors associated with the long-term treatment outcomes of real-world mental healthcare. This project – a participatory survey to investigate the long-term effectiveness of adult psychiatric services (PSILEAPS) – aims to address these questions. The survey will take place over a two-week period. It will be aimed at all five WL catchment area adult mental health units, and will cover care team members, service users and members of their social network. These will be asked to share their thoughts on (i) why mental health services have been needed in the case in question, and (ii) what factors in the treatment have been helpful or unhelpful. The service users who participate will form a research cohort, which will be followed over five years. Information on demographic and clinical characteristics will be obtained from social and healthcare registers at baseline, and at two- and fiveyear follow-ups. The primary outcome variables at follow-up will be treatment contact at follow-up, disability allowance at follow-up and death during follow-up. Exploratory statistical analyses will be used to study how different variables (including the main principles of OD) are associated with different outcomes. The information can be used to create new hypotheses to guide future research, and to develop mental health services. The participatory design will enable service users to join in the co-production of knowledge. This has the potential to immediately guide and improve their mental healthcare.