The aims of this study are to analyse the concept of mental health from the perspective of adolescent girls and boys and to describe what adolescent girls and boys regard as important determinants of mental health. Interviews with 48 children, 13 and 16 years old, in Sweden were held individually or in focus groups. The adolescents perceived mental health as an emotional experience, where positive as well as negative health is part of the concept. Family is the most important determinant for young people's mental health, closely followed by friends. Neither girls nor boys believed that there were any large differences in mental health between girls and boys. Age differences seemed to be more important than gender in the perception of mental health by children. (Contains 4 tables.)