Objective: This study explores the views of Finnish school personnel representatives regarding substance use prevention responsibilities. Design: Twenty-two focus groups were conducted within the scope of a regional intervention study in 2019. Qualitative content analysis was performed. Setting: Focus group interviews were conducted in the school setting. Subjects: Focus group participants included representatives for educational personnel and student welfare personnel working in basic education, general upper secondary education or vocational education settings. Main outcome measures: Views and experiences concerning roles and responsibilities in primary prevention of substance use. Results: Findings highlight the need for intersectoral efforts and intra-school collaboration in primary prevention efforts, but also in mental health promotion–on which the informants placed great emphasis. The health promotion leadership in schools, structural guidelines and the school curriculum could both challenge and support school personnel in their roles. An increased need to focus on the early years of life and related responsibilities of the homes was emphasized, along with the need to place more emphasis on health education in the first years of basic education, and responsibilities related to early risk identification. Conclusion: The findings highlight a need to develop structures and role clarity among school personnel, which can advance further development of intra-school and inter-sectoral collaboration in primary substance use prevention and mental health promotion. In the Finnish context, the successful implementation of relevant legislation, which some school representatives view as unclear or contravening, could be further supported.Key points Views regarding responsibilities in primary substance use prevention in the school setting have been less researched in the Nordic countries: The importance of inter-sectoral and intra-school collaboration is emphasized among school personnel representatives, including the role of the homes Primary prevention and mental health promotion responsibilities are viewed as less clear than secondary and tertiary prevention responsibilities Structural guidelines concerning e.g. confidentiality aspects and curriculum features can both support and challenge school representatives in their roles.