The prototype theoretical model for BPD fitted the data well and appeared to be satisfactory described by the current criteria. The emptiness criterion needs a more appropriate definition and the hierarchy of the criteria in DSM-IV should be revised.

These findings indicate that RF is associated with core aspects of personality pathology and capture clinically relevant phenomena in adult patients with PDs. Moreover, patients with different capacities for mentalization may need different kinds of therapeutic approaches.

Mentalization is the capacity to understand behavior as expressions of various mental states. It is assumed to be important for understanding the underlying psychopathology, the therapeutic process, and the outcome of therapy associated with patients with personality disorders (PDs). However, to date, empirical findings are scarce and inconsistent. This study aimed to examine whether the pre-treatment level of mentalization, operationalized as Reflective Functioning (RF), was associated with differential responses to two different treatment modalities and might predict clinical improvement. We analyzed data from a randomized clinical trial (Ullevål Personality Project). Seventy-eight patients with borderline and/or avoidant PD had been randomly assigned to either a step-down treatment program or outpatient individual psychotherapy. The step-down treatment comprised short-term day hospital treatment, followed by long-term, combined group and individual psychotherapy. RF was rated before treatment and after 36 months. Outcome measures were administered at baseline and after 8, 18, and 36 months. The moderator analyses indicated that patients with low RF levels at baseline responded better to outpatient individual psychotherapy than to the step-down treatment in terms of improvements in psychosocial functioning. Patients with medium-high RF levels responded equally well to both therapy formats. Determining which therapy format is appropriate for specific groups of patients can improve treatment efficiency. Therefore, our findings may have important clinical implications. Future research should address RF as a mediator of change.