Borderline Personality Disorder (BPD) is commonly recognised throughout theoretical and clinical accounts as one of the most challenging mental health disorders to treat however; there has been limited empirical investigation into characteristic psychologists reactions evoked by this diagnostic group. The aim of this study was to investigate cognitive and emotional responses of psychologists treating BPD. Method: Psychologists currently working with BPD clients gave informed consent to be interviewed regarding their responses to this client group. In addition, the Impact Message Inventory (IMI-C) and the Psychotherapy Relationship Questionnaire (PRQ) were completed. Transcripts from a semi-structured interview of psychologist's countertransference experiences were coded and scored to reflect core ideas and responses that were consistent across cases, whilst allowing for individual variation. Results: Major themes that emerged included significant psychologist anxiety and worry both before and after sessions, and confusion and frustration within the session in relation to implementing specific therapeutic tasks and skills. Self-report measures supported the transactional patterns found within the client-therapist dyad. The results from this study increase the current knowledge of common themes, origins and manifestations of countertransference reactions in the treatment of BPD, aiding psychologists to incorporate this clinically important information into the treatment process.