OBJECTIVE: The aim of this study was to determine the efficacy and safety of dialectical behavior therapy plus olanzapine compared with dialectical behavior therapy plus placebo in patients with borderline personality disorder. METHOD: Sixty patients with borderline personality disorder were included in a 12-week, double-blind, placebo-controlled study. All patients received dialectical behavior therapy and were randomly assigned to receive either olanzapine or placebo following a 1-month baseline period. RESULTS: Seventy percent of the patients completed the 4-month trial. Combined treatment showed an overall improvement in most symptoms studied in both groups. Olanzapine was associated with a statistically significant improvement over placebo in depression, anxiety, and impulsivity/aggressive behavior. The mean dose of olanzapine was 8.83 mg/day. CONCLUSIONS: A combined psychotherapeutic plus pharmacological approach appears to lower dropout rates and constitutes an effective treatment for borderline personality disorder.