Countertransference phenomena can be measured in clinically sophisticated and psychometrically sound ways that tap the complexity of clinicians' reactions toward their patients. Countertransference patterns are systematically related to patients' personality pathology across therapeutic approaches, suggesting that clinicians, regardless of therapeutic orientation, can make diagnostic and therapeutic use of their own responses to the patient.

Although difficulty with affect regulation is generally considered a core component of borderline personality disorder (BPD), surprisingly little research has focused on the nature of affect regulation and dysregulation in BPD. A random national sample of 117 experienced clinicians provided data on a randomly selected patient with BPD (N = 90) or dysthymic disorder (DD; N = 27). Clinicians described their patients using the Affect Regulation and Experience Q-sort-Questionnaire Version, a psychometric instrument designed for expert informants to assess affect and affect regulation. BPD and DD patients appear to differ in both the emotions they experience and the ways they regulate or fail to regulate them. Whereas DD patients are characterized by negative affect, BPD patients are characterized by both negative affect and affect dysregulation, which appear to be distinct constructs. BPD patients also show distinct patterns of affect regulation, and subtypes of BPD patients show distinct affect regulation profiles of potential relevance to treatment.

BPD in female adolescents resembles DSM-IV BPD as defined for adults. The operating characteristics of the DSM-IV criteria for adolescent boys require further investigation. Empirically derived subgroups are similar to those identified in recent research with adult females. Differences across subgroups on internalizing and externalizing Child Behavior Checklist (CBCL) scales provide preliminary data on the validity of subgroups and raise questions about the place of BPD among internalizing and externalizing spectrum disorders.

Borderline personality disorder patients in research samples are highly similar to those seen in a cross-section of clinical practice. However, several studies have now replicated a portrait of borderline personality disorder symptoms that places greater weight than the DSM-IV description on the intense psychological pain of these patients and suggests candidate diagnostic criteria for DSM-V.