Borderline personality disorder (BPD) is a serious chronic condition which may lead to a poor quality of life and carries a considerable risk of comorbidity and suicide. The syndrome has been acknowledged and investigated in psychiatry for at least seventy years. The DSM-IV gives a panel of nine symptoms and manifestations for its diagnosis, but not taking into account neurobiological and objective issues.The issue of whether BPD should be considered as a discrete condition, as the edge of a dimensional state ranging from 'almost normal' personalities to clearly pathological ones or as a hybrid of traits and symptomatic behaviors (McGlashan, 2005) seems to be important to correctly diagnose our patients and is a corner stone in the Research Agenda for DSM-V. The pathophysiology of BPD is very important because this is the progress which will probably lead to the development of effective treatments. Several investigators have shown some laboratory and objective clinical fi ndings in BPD as normality in endocrinological dynamic tests (De La Fuente et al., 2002), alterations in sleep-EEG parameters (De la Fuente et al., 2004), disturbed regional brain glucose metabolism (De la Fuente et al., 1997), abnormal scalp EEGs (De la Fuente et al., 1998) and an extremely high prevalence of neurologic soft signs (De la Fuente et al., 2006). These facts probably refl ect common underlying non focal nervous system failure and hypothalamic-pituitary-adrenal axis normality in BPD.However, these fi ndings are not pathognomonic of the condition and BPD is diagnosed according to DSM-IV when a patient shows at least fi ve symptoms out of a list of nine. First & Zimmerman (2006) propose that biological variables can aid to identify the patients as compared to the criteria used now to defi ne them. For this the objective signs and facts found in BPD could be included as diagnostic criteria in the DSM-V. Scalp wake EEG, the clinical exploration for neurologic soft signs, sleep EEG recordings and the two endocrine tests, dexamethasone suppression and TRH stimulation, which are cheap, not invasive and have shown to be linked to the diagnosis of BPD could be incorporated in a diagnostic weighting construct with these variables as additional score items. This would have at least three advantages over the present criteria: fi rstly, a part of the diagnosis of BPD would become objective, secondly, having these parameters would attach physiopathological information to the diagnosis and thirdly, the laboratory information and objective International Journal of Social Psychiatry.