Advances in genetic diagnostics lead to more patients being diagnosed with hereditary conditions. These findings are often relevant to patients’ relatives. For example, the success of targeted cancer prevention is dependent on effective disclosure to relatives at risk. Without clear information, individuals cannot take advantage of predictive testing and preventive measures. Against this background, we argue that healthcare professionals have a duty to make actionable genetic information available to their patients’ at-risk relatives. We do not try to settle the difficult (...) question of how this duty should be balanced against other duties, such as the duty of confidentiality and a possible duty not to know one’s genetic predisposition. Instead, we argue for the importance of recognising a general responsibility towards at-risk relatives, to be discharged as well as possible within the limits set by conflicting duties and practical considerations. According to a traditional and still dominant perspective, it is the patient’s duty to inform his or her relatives, while healthcare professionals are only obliged to support their patients in discharging this duty. We argue that this perspective is a mistake and an anomaly. Healthcare professionals do not have a duty to ensure that their patients promote the health of third parties. It is often effective and desirable to engage patients in disseminating information to their relatives. However, healthcare professionals should not thereby deflect their own moral responsibility. (shrink)