Adolescence as a time of bio-psychosocial transition confronts psychiatrists and psychotherapists with difficulties in diagnostics, crisis interventions and treatment especially with severely disturbed young persons. The diagnosis of Borderline Personality Disorder in adolescence has been avoided for years in order not to stigmatize adolescents. It was assumed that in adolescence it is difficult to differ between pathology and normality or borderline behavior and borderline disorder. Using a dimensional approach might now-a-day give a helpful orientation for the diagnosis of a Borderline Personality Disorder. The same is the case with identity diffusion as indicator. Further research is needed for the development of concepts of crisis intervention and psychotherapy of adolescents with Borderline Personality Disorder. Only few evaluated therapeutic studies of borderline treatment exist until today other than in treatment of adults. Experiences with Interventions in natural environments promoted by mobile units will be discussed. Furthermore special treatment concepts are necessary for severely disturbed adolescents with regard to their instable psychic state and instable life conditions. A psychodynamic therapeutic approach called PIM will be presented; the effectiveness of the method was shown in an inpatient RCT Study. Instead of taking the role of an expert the therapist acts as a resonant person expressing his experience in an answering mode in a symmetric relationship with the patient.