This paper reviews the history of the recognition of borderline personality disorder as a clinical disorder, followed by a review of the contemporary practice of diagnosing borderline personality disorder in psychiatric settings. Many researchers have cautioned against the conflation of difficult patients with the diagnostic category of borderline personality disorder. The current study examines how clinical indicators used to screen for this complex disorder differ across service settings, professions, specialised training and years of clinical experience. A purpose-designed survey was administered to 108 mental and emergency medicine health practitioners across an Australian health service and a New Zealand health service to record the level of significance placed on different clinical indicators in the application of the diagnosis of borderline personality disorder. A heavy reliance was placed on observable behavioural symptoms, such as self-mutilation and impulsive behaviours that are self-damaging, in the screening of borderline personality disorder as a psychiatric diagnosis. Statistically significant differences were found between emergency medical staff and mental health clinicians in their use of diagnostic indicators of borderline personality disorder, [chi][superscript 2](4) = 17.248, p = 0.002. Implications of these findings for the screening, assessment and diagnosis of patients with borderline personality disorder are discussed. (Contains 5 tables and 1 figure.)