Historical exclusion of personality disorders from the medical paradigm is reflected on the existence of the DSM-IV axis II for personality disorders. Personality disorders are perceived as substrates of vulnerability for axis I mental disorders such as depression, bipolar, anxiety or psychotic syndromes. A psychobiological perspective of this model of personality disorders is based on the study of genetic predispositions, of biological bases of personality traits and of the relationship of both with environmental precipitants.

Another psychobiological view of personality disorders is needed as a consequence of clinical evidence in borderline personality disorder (BPD). Most of the diagnostic criteria for this disorder are symptoms rather than traits and seem to be associated to several pathophysiological abnormalities. Serotonin dysregulation and glucocorticoid receptor dysfunctions among other biochemical findings have been reported in BPD. According to these biological findings, BPD could be included in a similar psychobiological framework than the axis I mental disorders.