This study investigated the relative efficacy of Mentalization-based therapy (MBT) and United Protocol (UP) in reducing symptoms of psychopathy and emotion dysregulation in a sample of Iranian community residents with concurrent diagnoses of antisocial and borderline personality disorders (PDs). Interpersonal, affective, and lifestyle features of psychopathy were measured post-treatment and at 6-, 12-, 18-, 24-, and 36-months follow-up using the 13-item version of the Psychopathy Revised-Checklist (PCL-R), which excluded, by design, criminal history features. Emotion dysregulation was measured using the Deficits in Emotion Regulation Scale (DERS) developed by Gratz and Roemer (2004). After treatment, both UP- and MBT-treated individuals showed significantly fewer features of psychopathy and significantly less emotion dysregulation. Compared with those treated with MBT, UP-treated individuals showed significantly less emotion dysregulation in all DERS subscales and a greater reduction in psychopathy features, particularly affective features. It is suggested that this likely reflected the particular emphasis placed by UP on improving emotional self-regulation and facilitating the therapeutic alliance. These results suggest that, despite the traditional pessimism that surrounds psychopathic individuals’ treatability, they can be successfully treated.