background  Dialectical behaviour therapy (dbt) is considered to be a promising treatment for patients with borderline personality disorder (bpd). However, the question is whether dbt can be regarded as the treatment-of-choice in the Netherlands for a mixed population of borderline patients with or without co-morbid substance abuse.

aim To investigate whether in the case of female bpd patients dbt is more effective than treatment-as-usual (tau) in reducing borderline symptomatology and substance abuse.

method Fifty-eight women with bpd, referred from addiction centres (n=19) and psychiatric services (n=39) were randomly assigned to either 12 months of dbt or 12 months of tau. Outcome measures included drop-out (treatment compliance), parasuicidal behaviour, self-damaging impulsive behaviour and substance abuse.

results Compared to tau, dbt resulted in lower drop-out rates (23% vs. 63%), less selfmutilating and self-damaging impulsive behaviour, and less alcohol abuse. At follow-up, 6 months after treatment had been discontinued, the benefits of dbt were still significantly more effective, but the size of the effect had become smaller.

conclusions dbt is superior to tau in reducing high-risk behaviour and alcohol abuse in patients with bpd. If the effect of dbt is to be maintained, the treatment needs to be continued.