Carers of persons with borderline personality disorder (BPD) experience high burden. Treatment guidelines advocate involving carers in comprehensive therapy approaches. This study is a randomized controlled trial of group psychoeducation, compared to waitlist. Group psychoeducation involved 6–8 carers per group and focused on improving relationship patterns between carers and relatives with BPD, psychoeducation about the disorder, peer support and self-care, and skills to reduce burden. Carers were randomized into intervention (N = 33) or waitlist (N = 35). After 10 weeks, those in the intervention reported improvements in dyadic adjustment with their relative, greater family empowerment, and reduced expressed emotion, sustained after 12 months. There were also improvements in carers' perceptions of being able to play a more active role, such as interacting with service providers. This study demonstrates that providing structured group programs for carers can be an effective way of extending interventions to a group experiencing high burden.