Borderline patients were compared with schizophrenic patients, neurotic depressed patients, and a group of patients with differing diagnoses. The purpose of this comparison was to find out whether borderline patients could be discriminated from other psychopathological groups and whether a discrete list of recognizable characteristics discriminating borderline patients could be isolated. According to the results of the comparison, borderline patients can be discriminated with high accuracy from matched comparison groups with whom diagnostic confusion is common. Seven criteria provided a clinically sensible and practical means of approaching the diagnosis of borderline disorder.