The legal duty to protect patient confidentiality is common knowledge amongst healthcare professionals. However, what may not be widely known, is that this duty is not always absolute. In the United Kingdom, both the General Medical Council governing the practice of all doctors, as well as many other professional codes of practice recognise that, under certain circumstances, it may be appropriate to break confidentiality. This arises when there is a wider duty to protect the health of others, and when the risk of non-disclosure outweighs the potential harm from breaking confidentiality. We discuss this situation specifically in relation to genomic medicine where relatives in a family may have differing views on the sharing of familial genetic information. Overruling a patient’s wishes is predicated on balancing the duty of care towards the patient versus protecting their relative from serious harm. We discuss the practice implications of a pivotal legal case that concluded recently in the High Court of Justice in England and Wales, ABC v St Georges Healthcare NHS Trust & Ors. Professional guidance is already clear that genetic healthcare professionals must undertake a balancing exercise to weigh up contradictory duties of care. However, the judge has provided a new legal weighting to these professional duties: ‘The scope of the duty extends not only to conducting the necessary balancing exercise but also to acting in accordance with its outcome’ [1: 189]. In the context of genomic medicine, this has important consequences for clinical practice.