This study examined the relationship between self-esteem and mental illness in a clinical group, consisting of children and adolescents, ages 10-18, who had been in contact with the child- and adolescent psychiatry. The participants (N=22) filled out the questionnaires “I think I am” and “Beck Youth Inventories”, which were used as measurements of perceived self-esteem and mental illness. These results were compared to a comparison group (N=299). The result of the study showed that children and adolescents in the clinical group reported a lower level of self-esteem and a higher level of mental illness compared to their peers. This indicated that there seemed to be a negative relationship between self-esteem and mental illness, and that self-esteem could act as an indicator of mental illness. Furthermore, self-esteem especially appeared to have a relationship to internalizing mental illness, such as depression and anxiety. The result also indicated that girls with mental illness tend to report lower self-esteem than boys with mental illness. The result was discussed in relation to practical implications and previous research.