The meaning of the diagnosis borderline depends on which borderline-concept is used (DSM-III, Gunderson and Kernberg). This article discusses how factors, such as model of treatment, kind of population and setting, influence the diagnostic process. From the absence of relevant validity-research one can conclude that the usefulness of the diagnosis borderline can not yet be proved. A study on validity of the DSM-III borderline-concept is presented. This study deals with the question whether there are differences between DSM-III borderline and neurotic patients with respect to: a. coping-strategies; b. results of treatment in a psychotherapeutic community. No differences between the two groups were found. For research on the validity of the borderline-concept, the use of Kernberg's concept is suggested.