Personality Organization Diagnosis, proposed by Dr. Otto F. Kernberg and his team from the Personality Disorder Institute in New York, has been an important contribution to the understanding and treatment of personality disorders. The aim of this article is to make an updated review of this approach, addressing a general understanding of what is personality, and subsequently deepening the differential diagnosis of the neurotic and borderline personality organization. Furthermore, within de borderline spectrum, those high, medium, and low functioning will be distinguished, considering its severity and prognosis. Finally, a synthesis of the personality assessment process will be carried put, which consist of the Structural Interview