Promoting patient autonomy has become a key imperative in health service encounters. We will examine the potential negative effects of over-promoting patient autonomy and consider the impact on patient access, their experience and the provision of equitable services by focusing on an extreme manifestation of this trend, i.e. calls for patient involvement in health care decision making to be mandatory. Advocates of mandatory autonomy hold that patients have a duty to themselves, to society and to the medical system to make decisions on their health care independently. Models of mandatory autonomy may be contrasted to those of optional autonomy that seek to ascertain patients’ decisional preferences and to understand wider limitations on their freedom to choose. Where choice as decisional responsibility becomes mandatory it ceases to promote agency and where autonomous choice is understood as an individualistic practice it will contribute to the cultural dominance of Western values. Moreover, taking a view that principlist ethics needs to take account of the social and cultural contexts of individual lives, we argue that if mandatory autonomy were to be over-emphasised as part of an ongoing move towards patient choice in UK National Health Service (NHS), educated and affluent people would be more able to exercise choices at the expense of people who are experienced in asserting preferences and who have the resources to make use of choices. We will argue that the promotion of autonomy needs to be tempered by steps to enable less powerful social, cultural and economic groups to contribute to decision making and to support individuals who may feel abandoned by having decisional responsibility transferred to them. Until constraints on individual choice can be understood and addressed, we advocate the model of optional autonomy used in shared decision making and make recommendations for practice, policy, education and research.