--- - |2+ Background Impulsivity is considered a core clinical feature in borderline personality disorder (BPD). Evidence also indicates that impulsivity is part of the biological vulnerability for BPD. The purpose of the study was to verify if the presence of substance‐related and addictive disorders (SRADs) may increase impulsivity and aggression in BPD. Methods Eighty patients (27 with BPD, 26 with BPD and SRAD, 27 with other personality disorders (OPDs)) completed a comprehensive assessment for personality disorder symptoms, impulsivity, and aggressive behaviour. Results BPD patients with SRAD showed higher scores on impulsivity and aggression compared with other groups. Furthermore, no significant difference was observed between BPD and OPD patients on impulsivity and aggression. Conclusion The presence of SRAD was found to be a mediator between BPD and impulsive and aggressive behaviour. The findings are discussed and directions for future research presented. - Clinical Psychologist, Volume 22, Issue 2, Page 211-219, July 2018.