Time-limited psychotherapy for depression is effective. However, comorbid personality disorders affect therapy outcomes negatively. Studies of follow-up effects and results relating to the influence of comorbid personality disorder and treatment modality are scarce.

To determine the influence of comorbid personality disorder and treatment modality on outcomes after cognitive–behavioural therapy (CBT) or short-term psychodynamic supportive psychotherapy (SPSP) for depression.

This study draws on data from a previously published randomised clinical trial contrasting SPSP and CBT for depression (both 16 sessions). We compared the effectiveness of these psychotherapies for patients with and without personality disorder (n = 196). The primary measure was depression outcome; the secondary measurements were interpersonal functioning and quality of life. Collected data were analysed using multilevel analysis. Trial registration: ISRCTN31263312 (http://www.controlled-trials.com).

Although participants with and without comorbid personality disorder improved at treatment termination (d = 1.04, 95% CI 0.77–1.31 and d = 1.36, 95% CI 0.97–1.76, respectively) and at follow-up (d = 1.15, 95% CI 0.87–1.43 and d = 2.12, 95% CI 1.65–2.59 respectively), personality disorder had a negative effect on depression outcome at both measurement points (P < 0.05). A similar negative effect on interpersonal functioning was no longer apparent at follow-up. Comorbid personality disorder had no influence on social functioning or quality of life outcomes, irrespective of treatment modality.

CBT and SPSP contribute to the improvement of depressive symptoms and interpersonal problems in depressed patients with and without comorbid personality disorder. Both treatments are an effective first step in a stepped care approach, but – given remaining levels of depression in patients with personality disorder – they are probably inadequate for large numbers of patients with this comorbidity.

None.