BACKGROUND: Although substance use is a common feature of borderline personality disorder, regular use is associated with greater levels of psychosocial impairment, psychopathology, self harm and suicidal behaviour and leads to poorer treatment outcomes. Management of co-occurring substance use disorder and borderline personality disorder within primary care is further compounded by negative attitudes and practices in responding to people with these conditions, which can lead to a fractured patient-doctor relationship. OBJECTIVE: This article provides an overview of how the general practitioner can provide effective support for patients with co-occurring borderline personality disorder and substance use disorder, including approaches to assessment and treatment, the therapeutic relationship, referral pathways and managing risk and chronic suicidality. DISCUSSION: Despite the complexities associated with this population, GPs are ideally placed to engage patients with co-occurring borderline personality disorder and substance use disorder in a long term therapeutic relationship, while also ensuring timely referral to other key services and health professionals. To provide the most effective responses to this patient group, GPs need to understand borderline personality disorder and its relationship to substance use, develop an 'explanatory framework' for challenging behaviours, implement mechanisms for reflective practice to manage negative countertransference, as well as learn skills to respond adequately to behaviours which jeopardise treatment retention.