Objective of this paper is to search for answers for the question if it is justified to use the diagnosis of personality disorder already in adolescence. Recent research data confirm that the stability of basic personality traits is only gradually lower in adolescence compared to adulthood. Using the diagnostic criteria of adults there is not much of a difference concerning prevalence rate and stability in adolescence and adulthood. Meta-analyses reveal that patients with personality disorders can successfully be treated with specalized treatment programs so that personality disorders should not be viewed as life-course persistent. It is argued that an early assessment with standardized procedures can help to identify adolescents with personality disorders so that specialized treatment approaches can be started. In adulthood there is empirical evidence for the use of Dialectical-Behavior Therapy DBT, Transference Focused Psychotherapy TFP, Mentalization-based Therapy MBT and Schema-focused Psychotherapy SFT for the use in patients with personality disorders. These treatment approaches have to be adapted to the special situation of adolescents so that their use can help to prevent these early developing disorders to become chronic.