This study aims to identify unusual experiences and psychiatric symptoms that indicate a heightened risk for severe mental disorders - especially psychoses. It is important to develop reliable questionnaire methods that are cost-effective in first-stage screening, leading to in-depth assessments and targeted care. However, existing psychosis-risk questionnaires are limited in content, intended for adults, and have been insufficiently tested for actual predictive value. Therefore we will collect a new, large dataset from an unselected group of adolescents entering psychiatric care in three major urban areas of Finland. Comprehensive national health care registers will be used to assess how well the selected experiences and symptoms predict the participants' mental health over the following few years.