Borderline personality disorder is a common and debilitating psychiatric disorder characterized by underlying disorders and dysfunction. Dialectical behavioral therapy has been developed to help borderline patients who have been introduced to the second level of treatment, intensive outpatient therapy with behavioral changes. The aim of this study was to evaluate the effectiveness of dialectical behavior therapy in reducing the morbid symptoms of patients with borderline personality disorder based on the three- factor theory of morbid symptoms. In this experimental study, 20 men with borderline personality disorder who were selected by availability sampling method were randomly assigned to experimental and control groups. After taking the pre-test, the participants in the experimental group underwent a course of dialectical behavior therapy, then the post-test was taken by both groups. After two months, a follow-up evaluation was performed. In all three stages, the severity index of borderline personality disorder was measured. The results of the study confirmed the effectiveness of dialectical behavior therapy on the three factors of borderline personality disorder (impaired communication, emotional dysregulation, and behavioral dysregulation) in both the post-test and follow- up stages (p ≤ .001).
