The interest in treating underlying core vulnerability factors or transdiagnostic processes has been a focus of much attention. In this paper we describe our application of group dynamic-relational psychotherapy to the treatment of perfectionism, a core personality vulnerability factor associated with various forms and types of dysfunction and disorders that have profound costs to the individual both socially and subjectively. Over the course of the past three decades, we developed an evidence-based integrative group treatment that targets the psychodynamic and relational underpinnings of perfectionism. The treatment is based on an integration of psychodynamic and interpersonal perspectives and therapeutic approaches. In this paper we present our model of perfectionism and describe our group dynamic-relational therapy for the treatment of its pernicious outcomes. By drawing on illustrative case material, we describe the approach as applied to one such group as it progresses through four phases of group development that we have termed engagement and pseudo attachment, pattern interruption, self-redefinition/painful authenticity, and termination. Finally, we present some of the accumulating evidence of the effectiveness and efficacy of dynamic-relational therapy.