Emotionally labile personality of borderline type (borderline personality) occurs in 1-2% of individuals from general population; 75% of this group are women. Similarly to most of the other mental disorders, the borderline personality results from a combination of biological, social and psychological factors. The subject of this study is a survey of the current knowledge on biological factors of borderline personality. Most researchers are of the opinion that these personality disorders are determined genetically, with such inherited temperamental traits as: dysregulation, impulsivity, and hypersensitivity. Perhaps hereditary is also a defect within the serotonergic system, endogenous opioid system and/or dopaminergic system related to the reward system. Many researchers have recently perceived the dysfunction of endogenous opioid system as an integral component of borderline personality. There is now a lot of evidence showing that this dysfunction as well as that of the reward system may account for most of the borderline personality symptoms which constitute an involuntary attempt of stimulating the inefficient systems. This is how e.g. the presence of reckless sexual behaviours, unstable interpersonal relationships and inability to delay the reward in borderline personality is accounted for. Such observations may in the future constitute an important indication for seeking a more effective pharmacotherapy for patients with borderline personality. It is possible that in some patients the described dysfunctions may be alleviated with time. This is implied by the results of comprehensive prospective studies which show a significant regression of symptoms and improvement in functioning of most patients with borderline personality after at least several years.