Background: Previous research has found that family environments high in expressed emotion, in particular emotional overinvolvement, are beneficial to the clinical outcome of patients with Borderline Personality Disorder (BPD). Aim: This study aims to investigate the relationship between expressed emotion, carer burden and carer wellbeing. Method: A total of 280 carers of a relative with BPD were administered the McLean Screening Instrument for BPD - Carer Version, The Family Questionnaire, Burden Assessment Scale and Mental Health Inventory. Results: Carers reported family environments high in expressed emotion, particularly criticism (82.9% of carers) and emotional overinvolvement (69.6%). Elevated emotional overinvolvement was correlated with higher burden and mental health problems. Conclusions: Elevated criticism and emotional overinvolvement in family environments represent a dynamic involving high conflict, anxious concern, overprotection and emotional closeness. The findings suggest that carers may benefit from intervention and support options considering the challenged interpersonal dynamic, burden and impaired carer wellbeing reported in this study.