Objectives. Dialectical behavioral therapy (DBT) has gained widespread popularity as a treatment for borderline personality disorder (BPD), and its efficacy has been demonstrated in several trials. The aim of this study was to evaluate the effectiveness of DBT delivered by staff with a level of training readily achievable in National Health Service care settings for individuals with a Cluster B personality disorder.

Design. Randomized control trial methodology was used to compare DBT to treatment as usual (TAU).

Method. Forty-two participants entered the trial. Diagnostic and outcome measures were undertaken at assessment, at 6 months, and at 1 year. The clinical outcomes in routine evaluation – outcome measure (CORE-OM) were utilized as the primary outcome measure.

Results. Both the DBT and TAU groups improved on the range of measures employed. The DBT group showed a slightly greater decrease in CORE-OM risk scores, suicidality, and post-traumatic stress disorder symptom severity. However, the TAU group showed comparable reductions in all measures and a larger decrease in para-suicidal behaviours and risk.

Conclusions. DBT may be an effective treatment delivered by community outpatient services for individuals with a Cluster B personality disorder. Further studies are needed to consider the impact of experience and adherence to DBT in improving outcome.