The concept of borderline personality disorder is a most controversial issue within clinical psychiatry. The American DSM-III-R’s (1988) circumscribed, descriptive definition seems to correlate with the future European ICD-10. However, the most vigorous contributors to a dynamic and structural understanding of borderline personality disorder as well as the ‘treatment of choice’ are Kernberg, Gunderson and Masterson. They agree on these patients’ lack of consistency, being ‘stable in their instability’. The dilemma is how to integrate their findings in a more uniform concept that makes research and clinical practice comparable, reliable and valid on a national as well as on an international basis. © 1991 Taylor & Francis Group, LLC.