The definitional criteria of the 3 systems (DSM-III, DIB and Kernberg) have been compared. While there is rather weak agreement between the criteria of DIB and those of DSM-III, there is no agreement at all between Kernberg's criteria and those of the other 2 systems. When the 3 systems are compared in terms of empirical diagnosis, the agreement between DSM-III and DIB is moderate and clearly stronger than that between Kernberg and either DSM-III or DIB. In terms of sensitivity, the Kernberg borderline comprises the DSM-III and DIB borderlines as subsets. The findings are consistent with the idea that Kernberg's borderline concept is an instance of a severity or maturity level construct, while DSM-III and DIB are characterological constructs, orthogonally related to the level construct.