The aim of this study is to assess whether impulsive and aggressive traits can be placed on a continuum with DSM-IV Cluster B Personality Disorders (PDs) and to determine if different aspects of these personality traits are specifically associated with individual Cluster B PDs. The study group comprised 461 outpatients admitted consecutively to a clinic that specializes in the diagnosis and treatment of PDs. Principal component analyses clearly suggested a five-factor structure of both normal and psychopathological personality traits. Importantly, measures of impulsivity, aggressiveness and novelty seeking formed a part of the principal component that clustered all Cluster B PDs. Regression analyses indicated that impulsive traits were selectively associated with Borderline PD whereas different aspects of aggressiveness were useful in discriminating Narcissistic PD from Antisocial PD. Sensation seeking traits formed a part of Histrionic PD. These results indicate that impulsive/aggressive traits may be useful in explaining both why Cluster B PDs tend to covary, and why they frequently differ in clinical pictures and courses.