The specificity and the severity of psychopathology in adolescence often requires a highly complex observational setting. This is due to the important role which the setting plays in every diagnostic and therapeutic intervention concerning adolescents with severe personality disorders. This larger context entails the creation of a setting which will reveal the interactional style of the adolescent as it is expressed spatially, temporally, through relationships and learning skills. In this paper, we will present a methodological illustration of the role played by the institutional setting in the diagnostic and therapeutic process.