Children spend a lot of time in school during their childhood and it is important that schools are safe and good environments. Though, mental illness among pupils in Sweden continues to increase. The education act (SFS 2010:800) states that schools and especially school counselors should work with health promotion and prevention with primarily mental illness, even if the content of such prevention remain a bit unclear. The aim of this study was to describe and analyze how school counselors talk about prevention as part of their work to counter mental illness among pupils. The study has a constructionistic approach and method used is qualitative interviews, where the interviewees are school counselors.School counselors express knowledge about mental illness, but underline a need to continuously learn more about young people’s living conditions and how to prevent mental illness. The school counselors are consistent about the importance of working preventively against mental illness in school, a work which they see as unclear and primarily construct as being present among pupils and group activities. However, obstacles are perceived within school organizations to carry out such preventive work, which relate to ad hoc tasks, scarce resources, unclear guidelines and challenging collaboration with other professional groups in the school.