The Borderline Personality Disorder (BPD) diagnosis was originally introduced in DSM-III as a new category separated from the other “borderline” condition of schizotypal personality disorder. Until this point, the “borderline” concept had served as a metaphor for conditions on the border to schizophrenia and mood disorders. The “borderline” concept was, thus far, a well-established severity indicator for any marked character disorder, which was now turned into a distinct category or syndrome including diverse symptoms such as mood and identity problems, self-mutilating behavior, feelings of emptiness, and episodic aggression. In a 2016 interview, “the father” of BPD, John Gunderson, offered a candid reflection about the initial conception (and perhaps vagueness) of the BPD diagnosis:

“A group of patients that didn’t have a diagnosis, but which drove everybody crazy.”

In contrast to the unspecific borderline continuum, it became possible to use specific diagnostic criteria to recruit patients for research and treatment programs as done with other specified disease entities.