Mental illness continues to increase, and it is a societal problem that involves many young people. Young people often spend large parts of their upbringing in school and thus this is a place where mental illness becomes particularly evident. School counselors are psychosocial experts who, according to SFS 2010:800, must work to promote health and prevent mental illness. On the other hand, there are organizational challenges in the school counselors' work that prevent them from working as much preventively as they really needed. The aim of the study is therefore to increase understanding of how the school counselors experience their preventive work against mental illness. The study has been based on a qualitative method and is primarily based on the eight interviews held through a semi-structured interview method. The interviewees in the study are school counselors and are all active in Sweden, both women and men. The school counselors express that mental illness is mainly very individual, but that there are also patterns in many cases of how the mental illness expresses itself. There is a connection in the answers of the interviewees to the fact that there are a lot of organizational challenges in the conditions for working preventively against mental illness. The challenges are mainly about lack of time, uneven distribution of resources, unclear guidelines, and a lack of cooperation with other professionals both internally and externally.