There is a growing conversion, confusion and controversy in clinical psychiatry concerning the usage of the borderline concept. An increasing number of hospitalized patients are classified as borderline conditions. This expansion and popularity of the borderline concept has many explanations and historical roots: the notion of a continuum of mental disorders, the concept of forme fruste of psychotic illnesses: clinicians' uncertainty as to where to categorize some difficult patients--a nondiscriminatory synonym; the psychoanalytic establishment--and decline--in clinical psychiatry in the United States; a field for ideological battles between psychodynamic and biological oriented schools of psychiatry, etc. In ICD-10, the borderline conditions are hierarchically divided and outlined in clinical description and diagnostic guidelines into schizotypal disorder and emotionally unstable personality disorder--impulsive or borderline subcategory. This closer demarcation of prototypes in the classification system may facilitate less confusion in future. All Scandinavian countries have contributed a great deal to the research in the field of borderline conditions, especially with regard to genetic and nosological issues. A brief summary of these contributions is presented. Some important notions in the phenomenologic and prototypically oriented European tradition of classifying personality disorders are explained in order to understand the rather ambiguous reaction to the borderline concept in European countries.