This article explores which aspects of the clinical presentation of psychopathology in borderline personality disorder (BPD) might be thought to be most closely linked to a history of childhood sexual abuse (CSA). The article describes which particular types of sexual abuse experiences are thought to be most prevalent in patients with BPD, and proceeds to review our current understanding of the biological substrates that may be involved in the clinical picture of BPD. The article then turns to the concept of trauma, and examines what are thought to be the biological underpinnings and/or reactions to trauma (particularly with respect to Post Traumatic Stress Disorder) and, by extension, to overwhelming and/or chronic stress, while making the logical assumption that childhood sexual abuse can be categorized most understandably as trauma. Finally, the article tries to integrate these observations by pulling together the commonalties of the biology of stress and trauma with the biology of BPD, in order to put forth an hypothesis as to the possible implications of a history of childhood sexual abuse upon the biology of BPD. The article concludes that the type and breadth of the patient with BPD's hyperreactivity to the environment, which often manifests itself as hypersensitivity in interpersonal situations, is probably mediated through noradrenergic mechanisms, and these processes may be most closely related to a history of CSA. On the other hand, impulsivity, which is related to serotonergic mechanisms, is the major constitutional predisposition to BPD, regardless of whether or not there is a history of trauma. Combining environmental hyperactivity with impulsivity may lead to a clinical picture, often seen in BPD, where impulsivity and self-destructive behavior is employed in order to deal with the stress, distress, and dysphoria of being hypersensitive to interpersonal and other environmental stimuli.