The notion of respect for autonomy dominates bioethical discussion, though what qualifies precisely as autonomous action is notoriously elusive. In recent decades, the notion of autonomy in medical contexts has often been defined in opposition to the notion of autonomy favoured by theoretical philosophers. Where many contemporary theoretical accounts of autonomy place emphasis on a condition of "authenticity", the special relation a desire must have to the self, bioethicists often regard such a focus as irrelevant to the concerns of medical ethics, and too stringent for use in practical contexts. I argue, however, that the very condition of authenticity that forms a focus in theoretical philosophy is also essential to autonomy and competence in medical ethics. After tracing the contours of contemporary authenticity-based theories of autonomy, I consider and respond to objections against the incorporation of a notion of authenticity into accounts of autonomy designed for use in medical contexts. By looking at the typical problems that arise when making judgments concerning autonomy or competence in a medical setting, I reveal the need for a condition of authenticity-as a means of protecting choices, particularly high-stakes choices, from being restricted or overridden on the basis of intersubjective disagreement. I then turn to the treatment of false and contestable beliefs, arguing that it is only through reference to authenticity that we can make important distinctions in this domain. Finally, I consider a potential problem with my proposed approach; its ability to deal with anorexic and depressive desires.