In a recent article Thomas May has argued that the use of advance directives (ADs) to respect a no longer competent patient's autonomy is a failed strategy. Respect for patient autonomy is clearly one of the guiding moral principles of modern medicine, and its importance is reflected in medical emphasis on informed consent. Prima facie, at least, ADs seem likewise to respect patient autonomy by allowing patients to make decisions about treatment in advance of situations in which the patient may no longer be able to specify the form of treatment desired. So a claim that ADs do not extend patient autonomy to these situations of diminished competence represents a serious criticism of our understanding not only of advance directives, but of autonomy as well.