This article critically re-examines the application of the principle of patient autonomy within bioethics. In complex societies such as those found in North America and Europe health care professionals are increasingly confronted by patients from diverse ethnic, cultural, and religious backgrounds. This affects the relationship between clinicians and patients to the extent that patients' deliberations upon the proposed courses of treatment can, in various ways and to varying extents, be influenced by their ethnic, cultural, and religious commitments. The principle of (...) patient autonomy is the main normative constraint imposed upon medical treatment. Bioethicists typically appeal to the principle of patient autonomy as a means for generally attempting to resolve conflict between patients and clinicians. In recent years a number of bioethicists have responded to the condition of multiculturalism by arguing that the autonomy principle provides the basis for a common moral discourse capable of regulating the relationship between clinicians and patients in those situations where patients' beliefs and commitments do or may contradict the ethos of biomedicine. This article challenges that claim. I argue that the precise manner in which the autonomy principle is philosophically formulated within such accounts prohibits bioethicists' deployment of autonomy as a core ideal for a common moral discourse within multicultural societies. The formulation of autonomy underlying such accounts cannot be extended to simply assimilate individuals' most fundamental religious and cultural commitments and affiliations per se. I challenge the assumption that respecting prospective patients' fundamental religious and cultural commitments is necessarily always compatible with respecting their autonomy. I argue that the character of some peoples' relationship with their cultural or religious community acts to significantly constrain the possibilities for acting autonomously. The implication is clear. The autonomy principle may be presently invalidly applied in certain circumstances because the conditions for the exercise of autonomy have not been fully or even adequately satisfied. This is a controversial claim. The precise terms of my argument, while addressing the specific application of the autonomy principle within bioethics, will resonate beyond this sphere and raises questions for attempts to establish a common moral discourse upon the ideal of personal autonomy within multicultural societies generally. (shrink)