Objective. The aim of this open-label 8-week study was to assess the effectiveness of quetiapine on aggressive behaviour and social dysfunctions in patients suffering from a cluster B personality disorder (DSM-IV). Methods. The visits were performed at baseline and at days 14, 28 and 56. After a standard titration schedule, the patients received a dose augmented or reduced dose, within a range from 50 to 400 mg/day during the visits, depending on efficacy and tolerance. Assessment of efficacy was based on the French version of the Social Disability and Aggression Scale SDAS (SDAS-21). Response was defined as a decrease of 50% reduction of the total scores compared to baseline. Tolerability was assessed with the CGI, UKU, EPS-scales. Results and conclusion. Eight of the 12 patients included received 200 mg/day quetiapine after titration (all patients: 50-400 mg/day). At week 8, five out of 12 patients were responders based on the SDAS-21 scores for the average expression of the symptoms, and six out of 12 on the basis of SDAS-21 scores for the peak expression. There was a significant correlation between weight change and total SDAS variation (Kendall's b= -0.644; p=0.02). These findings should be reexamined in further studies.