As elsewhere in the Western world there has been an ardent discussion in recent years in Denmark concerning the validity of the borderline diagnosis. The present study examines several demographic variables for patients diagnosed with specific personality disorders admitted to Danish psychiatric departments in the years 1975, 1980, and 1985. The total numbers of patients admitted were largely unchanged, but the prevalence of the borderline diagnosis increased from 5% to 20%. For males, it appears that those who had previously been diagnosed as psychopathic deviants are now labeled as borderlines. The shift is less distinct for females; in general, women diagnosed borderline today would likely have been labeled immature, hysterical, or psychopathic in 1975. It is clear that explicit diagnostic criteria for personality disorders must be employed if epidemiologic trends are to be determined, especially among new categories such as the borderline. Otherwise it will be difficult to know if changes in diagnostic use are truly related to social changes or merely to new theoretical or professional predilections.