In 2021, the Swedish Agency for Health Technology Assessment and Assessment of Social Services (SBU) published an inventory, which identified over 2000 evidence gaps in mental health1 from the two known international database of evidence gaps: the SBU Evidence Gap database, which is continuously updated, and the former UK Database of Uncertainties about the Effects of Treatments. Within the framework of a Swedish governmental commission on mental health, we conducted a priority setting partnership to assess which of the identified evidence gaps regarding serious mental illnesses (SMI)2 were most urgent to address. A similar project regarding common mental illness is also envisioned. The aim of the current priority setting was to identify what patients, carers, clinicians and practitioners consider to be the most important outstanding research questions in the care of SMI. The interventions studied include prevention, diagnostics, treatment, support and social care, service delivery and coordination of healthcare and social care. Target groups for the report are researchers, research funders, government agencies and authors of systematic reviews.