Abstract The refusal of medical treatment is a recurrent topic in bioethical debates and Jehovah's Witnesses often constitute an exemplary case in this regard. The refusal of a potentially life-saving blood transfusion is a controversial choice that challenges the basic medical principle of acting in patients' best interests and often leads physicians to adopt paternalistic attitudes toward patients who refuse transfusion. However, neither existing bioethical nor historical and social sciences scholarship sufficiently addresses experiences of rank-and-file Witnesses in their dealings with the health care system. This article draws on results of a nine-month (2010, 2011–2012) ethnographic research on the relationship between religious, legal, ethical, and emotional issues emerging from the refusal of blood transfusions by Jehovah's Witnesses in Germany (mainly in Berlin). It shows how bioethical challenges are solved in practice by some German physicians and what they perceive to be the main goal of biomedicine: promoting the health or broadly understood well-being of patients. I argue that two different understandings of the concept of autonomy are at work here: autonomy based on reason and autonomy based on choice. The first is privileged by German physicians in line with a Kantian philosophical tradition and constitutional law; the second, paradoxically, is utilized by Jehovah's Witnesses in their version of the Anglo-Saxon Millian approach.