This article explores the process through which the advances of genetic research are incorporated into public health care in Denmark. Drawing on ethnographic fieldwork in cancer genetic counselling, the implementation of new medical advances is investigated by following the establishment of a policy on informing relatives at risk of hereditary cancer. This case material provides the occasion to examine how policies are shaped in a governmental process through which different actors seek to establish a common goal for a specific health practice. The struggle to define such a goal implies a struggle to define where to draw the line between health and disease and what makes up a healthy person in the context of genetic knowledge. The authors argue that in the process of establishing a policy in the field of cancer genetics the imperative of prevention comes to provide the framework within which an ethics of rights and responsibilities is constituted and the target group of cancer genetic counselling defined. This ethics is not determined by or inherent in genetic technology itself, but constituted in a social process and therefore negotiated within pre-existing frameworks of understanding in professional practice.