In the present thesis “Mothers teardrops on the floor, she doesn’t have her Hänschen no more” The mental disease of parents and its impact on the development of adolescents, the subject of mental disease, particularly the borderline personality disorder of a parent in addition of the development- and the resulting detachment process of adolescents will be treated. Main signs of adolescence are shown and a definition of this part of age is essential for the thesis. With the ICD 10 a definition of the borderline personality disorder and also an overview of behavior an therapy possibilities of diseased is given. The development of children is affected by such a disease, and growing up with a mentally diseased parent may, in addition to the increased risk of developing the disease themselves, have long-term consequences, shown in examples of choosing work and partner. At the end of the thesis, attention is given to the field of social work and pedagogy to have a sensible view on the topic of mental disease and possibilities of action.