The rule that a patient should give a free, fully-informed consent to any therapeutic intervention is traditionally thought to express merely a right of the patient against the physician, and a duty of the physician towards the patient. On this view, the patient may waive that right with impugnity, a fact sometimes expressed in the notion of a right not to know. This paper argues that the rule also expresses a duty of the patient towards the physician and a right of the physician against the patient. The argument turns, first, on the truism that a physician has no obligation to commit a battery, or unauthorized touching, and, second, on the thesis that a patient necessarily cannot consent to something that is unknown to him. The conclusion is drawn that a patient is not free to receive treatment voluntarily without knowledgeably authorizing it.