Abstract: This report presents efficacy and safety outcomes for patients with borderline personality disorder (BPD) treated with olanzapine for up to 24 weeks. In 2 concurrent studies, patients received open-label olanzapine for 12 weeks after 12 weeks of double-blind olanzapine or placebo. Open-label dosing started at 2.5 or 5 mg/d and could be increased up to 20 mg/d (study 1) or 15 mg/d (study 2). The primary efficacy measure was open-label baseline–to–endpoint change in Zanarini Rating Scale for BPD (ZAN-BPD) total score. Of 472 patients who completed the double-blind acute phase, 444 entered and 320 (72.1%) completed 12 weeks of open-label extension treatment. Mean ZAN-BPD total scores at the start of the acute phase were approximately 17, indicating moderate symptom severity. Mean ZAN-BPD total scores ranged from 7.8 to 10.5 at the start of the open-label treatment and decreased to 5.7 to 6.5, indicating mild symptom severity, by the end of the open-label treatment. Patients taking placebo during the acute phase showed increases in weight, prolactin level, and other laboratory values during open-label olanzapine treatment similar in magnitude to increases seen in olanzapine-treated patients during the acute phase. Patients proceeding from olanzapine during the acute phase to open-label olanzapine showed smaller changes in weight and laboratory values. In conclusion, these results suggest that continued therapy with olanzapine may sustain and build upon improvements seen with acute olanzapine treatment of patients with BPD. However, no medication is currently approved for treatment of BPD, and physicians should carefully weigh potential benefits and risks of antipsychotic treatment in this population.