Borderline Personality Disorder (BPD) is a psychiatric diagnosis in the Diagnostic and Statistical Manual of Mental Disorders IV that describes a prolonged disturbance of personality function characterized by depth and variablity of moods. The disorder typically involves unusual levels of instability in mood; "black and white" thinking, or "splitting"; chaotic and unstable interpersonal realtionships, self-image, identity, and behaviour; as well as a disturbance in the individual's sense of self.

It is far more common in women than in men, by a ration of about three to one. Its cause is controversial, with theories ranging from abuse and neglect, through genetic predisposition, to brain abnormality.

Not unreasonably, these disturbances can have an overall negative impact on many or all of the areas of life, especially in relationships. This includes difficulties maintaining relationships in work, home and social settings. Attempted suicide and completed suicide are common outcomes, especially without proper care and effectively therapy.

Onset of symptoms typically occurs during adolescence or young adulthood. Symptoms may persist for several years, but the majority of symptoms lessen in severity over time, with some individuals fully recovering. The mainstay of treatment is various forms of psychotherapy, although medication and other approaches may also improve symptoms.

While BPD can manifest irself in children and teenagers, therapists are discouraged from diagnosing anyone before the age of 18, due to adolescence and a still-developing personality.

It should also be noted that BPD is a bit of a 'catch-all' diagnosis, and is often used to describe someone with erratic relationships and mood difficulties. Recently, BPD as a diagnosis is being seen as stigmatising, especially to women, and there is a move to change the diagnosis in future. Over its history, BPD has gradually migrated from being a subset of psychotic diagnosis to a difficulty in its own right, and may end up in time being seen as a trauma or neglect diagnosis.