Young people at risk of developing borderline personality disorder (BPD) experience significant distress and loss of social function in the context of emotion dysregulation, relationship problems and deliberate self-harm. The evidence base for effective intervention for such emergent difficulties is sparse. We adapted a mentalization-based therapy manual originally developed for adults with BPD for our at risk adolescent population (MBT-A). Early evaluation suggests this treatment is acceptable to adolescents and may result in reduced crisis presentations. We now aim to establish its clinical efficacy through a pilot RCT comparing MBT-A to treatment as usual (TAU) to determine: effectiveness of recruitment strategies; compliance with protocol/procedures; trends towards reduced self-harm. Results will inform a definitive future RCT and potential for wider service implementation.