Objective: This study reports the six-year follow-up data of patients with borderline personality disorder (BPD) who participated in the Ulleval Personality Project (UPP), a randomized clinical study comparing outpatient individual psychotherapy (OIP) with a long-term combination programme (CP) comprising short-term day-hospital treatment followed by outpatient combined group and individual psychotherapy. Methods: For 52 patients, outcomes were evaluated after 8 months, 18 months, 3 years, and 6 years based on a wide range of clinical measures, such as symptom severity, psychosocial functioning, personality functioning, and Axis-I and II diagnoses. Results: At the six-year follow-up, patients in the CP condition reported significantly greater reduction of symptom distress and improvements in the personality functioning domains Identity Integration and Self-control compared with patients allocated to OIP. Patients in the CP also had a more favourable long-term course of psychosocial functioning. There were no differences between treatment conditions in outcomes of interpersonal functioning and self-esteem. Conclusions: Long-term psychotherapy in a combination programme seems favourable for BPD patients. In this study, patients who received combined treatment fared better on crucial parameters than patients who received individual therapy. Of particular importance are the positive effects on fundamental borderline problem areas like Identity Integration and Self-control.