Borderline personality disorder is a mental disorder characterized by: inadequate emotional regulation, impulsivity, risk behavior, irritability, feeling of emptiness, self-destruction and fear of abandonment as well as unstable interpersonal relationships. The history of this disorder dates back to the 17th century, but it is only at the end of the 20th century that it has been included in medical classification systems. Today, these valid classification systems suggest the exact diagnostic criteria that need to be fulfilled in order to establish a definitive diagnosis of this disorder. This diagnosis is most commonly found in adults, but there are numerous facts that support diagnosis of this disorder in children and adolescents. In children and adolescents, borderline personality disorders are most often manifested by affective instability, impulse control disorders, identity disorders, and self-destructive behavior. The same can be said for borderline personality disorder and in adulthood. Also, statistical data show that the prevalence of borderline personality disorder in childhood and adolescence is comparable to those in adulthood. The exact causes of borderline personality disorder are still not quite known, but today it is considered to be caused by several factors: genetics and environmental factors. Among the environmental factors, traumatic experiences in childhood play a leading role. The basis for treatment of this disorder is psychotherapy. Positive effects of psychotherapy are evident not only in increasing the potential for positive treatment outcome, but also in changing the individual's epigenetic status. Timely diagnosis and earlier treatment initiation increase the possibility that people with borderline personality disorder will enter the remission of the disease, as they reduce the possibility of fatal consequences such as suicide. In accordance with all the above-mentioned, borderline personality disorder should be diagnosed immediately after recognizing the symptoms, regardless of age.