The notion of "mediation" has profoundly transformed clinical approaches aiming at a change either in knowledge, in the way of being or of behaving. The way to treat narcissistic-borderline adolescents in the long-term in a secure hospital does not escape this notion. Until now, the psychodynamic-analytical approach has been the only one presenting interventions in such context, and this, since many decades. The present article attempts to witness the evolution of the clinical approaches within the Quebec security-hospital milieu, and to translate in E.J. Young's cognitive language part of the clinical work currently done. The active and mediation role of the clinical intervenor (including the psychotherapist) constitutes the guiding line of the gradual transformation of approaches.