This short paper examines the relationship between borderline psychopathology and various theories regarding the aetiology of this disorder. In the formation of borderline personality organization, distinct structural alterations in personality development are thought to arise from both genetic/neurobiological and environmental/trauma factors. We concur that these variables are instrumental in the formation of borderline personality organization. However, we believe that genetic/neurobiological variables are more closely related to developmental deficits, whereas environmental/trauma factors are primarily associated with either arrested development or regressive phenomenon. Regardless of aetiology, the resultant borderline personality organization disorders may present with comparable symptoms. Further, we hypothesize that the prognosis for response to treatment is related primarily to whether the borderline disorder arises from developmental deficits, arrested development, or regressive phenomena. Diagnostic indicators and treatment considerations for each of the borderline aetiologies are presented.