Adult attention deficit hyperactivity disorder (ADHD) is frequently associated with borderline personality disorder (BPD). As both disorders share some core clinical features they are sometimes difficult to distinguish from one another. The present work aimed to investigate differences in the expression of impulsivity, anger and aggression, quality of life as well as the number and severity of the comorbidities between ADHD, BPD, comorbid BPD-ADHD and control subjects. ADHD and BPD-ADHD patients showed a higher level of impulsivity than BPD and control subjects. BPD-ADHD patients had higher levels of substance abuse/dependence and higher levels of aggression than the other groups. Comorbid BPD-ADHD patients showed high levels of impulsivity and aggression, a characteristic that should draw the attention of clinicians on the necessity of providing an accurate diagnosis. The question also arises as to whether they represent a distinct clinical subgroup with specific clinical characteristics, outcomes and vulnerability factors.