Emotionally Unstable Personality Disorder is a complex and often stigmatising diagnosis. Although falling under the remit of mental health services, it is not always seen as a mental health need and research suggests that, if parents or carers are not provided with more holistic support, parental mental health will deteriorate with children likely to have poorer outcomes, placing them at an increased risk of harm. This likelihood of harm increases with compounding factors such as substance misuse and domestic abuse. One organisation alone cannot effectively address the complex difficulties that people with this diagnosis may experience, thus interagency working is necessary. This paper explores the barriers and facilitators to interagency working to support parental caregivers with a diagnosis of Emotionally Unstable Personality Disorder between Children’s Social Care and a Community Mental Health Team within the same English area. Five mental health care coordinators and two children and families social workers who had experience working with this client group were interviewed. Participants identified challenges and benefits to working with their partner agency around communication, knowledge, stigmatisation and resources. The research provides suggestions to develop current interagency working relationships and to enhance care and support available to people experiencing the diagnosis.