Since the introduction of a separate axis in DSM-III (1980), the validity of the categorical nature of the classification of personality disorders has been seriously questioned. Subsequently, a number of multidimensional alternatives have been proposed based on statistical procedures or theoretical considerations. At the same time, the study of the neurobiological underpinnings of personality and personality disorders has created a better understanding of etiological and pathogenetic processes responsible for these chronic disorders. The findings of these studies corroborate some of the major findings of statistical studies regarding the nature of the frequent comorbidity of axis II disorders. In the discussion, a mixed, two-tier diagnostic model is proposed to serve both scientific and clinical aims without the disadvantages of an exclusive choice for either categorical or dimensional approaches to the classification of personality pathology.
