Borderline personality disorder (BPD) is a condition that has a high mortality and is associated with much distress for the sufferers as well as with difficult management problems for health professionals. In this study 28 female cases of BPD and 20 normal females compatible for age and social status (control group), consented to perform the research. The research included a semi-structured intenriew, "Hamilton Checklist of symptoms of depression", "Beck Depression Inventory", serum cholesterol, prolactine, c;)rtisol and serotonine. Immunological study included "Interleukin-6" and neurophysiological study included electroencephalography (EEG ). Results revealed significant prevalence of impulsivity, affective instability, unstable relationship, self-mutilation behavior, inappropriate anger, suicidal trials, sexual relations and substance abuse among cases of BPD. Childhood abuse during childhood especially sexual one was evident_ Mood disorders were found to be significantly co-morbid with BPD. Results of Hamilton and Beck psychometric tests revealed significant depressive manifestations among cases than among control group. Biological studies proved higher level of cholestrol, prolactine and serotonine than control but their serum levels were within normal ranges. Cortisol level was lower in cases of BPD but within normal range too. Immunological study revealed significant lower level of "Interleukine-6" than ~ control group and its level were below average. EEG study showed some changes in some cases without significance. We found that BPD is under-diagnosed or misdiagnosed and sometimes its presence may be the result of poor prognosis in cases of mood disorders. We empathized also the importance of its diagnosis in other conditions like substance abuse and suicidal behavior.