Guidelines of the American Psychiatric Association for borderline personality disorder (BPD) indicate selective serotonin reuptake inhibitors and the serotonin and noradrenaline reuptake inhibitor (SNRI) venlafaxine for treating affective dysregulation and impulsive behavioural dyscontrol symptoms. The SNRI duloxetine has been studied in patients with major depression, generalized anxiety disorder and fibromyalgia, showing particular efficacy on somatic complaints. This study investigates duloxetine in the treatment of patients with BPD. Eighteen outpatients with a DSM-IV-TR diagnosis of BPD were treated with open-label duloxetine, 60 mg/day, for 12 weeks. Patients were assessed at baseline, week 4 and 12 with the CGI Severity item, the BPRS, the HAM-D, the HAM-A, the SOFAS, the BPD Severity Index (BPDSI) and the HSCL-90-Somatization Subscale (HSCL-90 SOM). Adverse effects were evaluated using the Dosage Record Treatment Emergent Symptom Scale. Statistics were performed with the analysis of variance. Significant P values were <or=0.05. Fourteen patients completed the study. Four patients (22.2%) discontinued treatment in the first 4 weeks because of non-compliance. A significant change was found for: BPRS, HAM-D, SOFAS, BPDSI total score and items 'impulsivity', 'outbursts of anger' and 'affective instability' and HSCL-90 SOM. Adverse effects were mild headache and nausea. Initial results suggest that duloxetine is an effective and well-tolerated treatment for BPD, with positive effects on somatic symptoms.