It is generally held that doctors and researchers have an obligation to obtain informed consent. Over time there has been a move in relation to this obligation from a requirement to disclose information to a requirement to ensure that that information is understood. Whilst this change has been resisted, in this article I argue that both sides on this matter are mistaken. When investigating what information is needed for consent to be informed we might be trying to determine what information a person would need in order to consent at all, or we might be trying to determine what information a person needs in order to make an informed choice about whether or not to consent. I argue that the obligation to ensure understanding only applies to information generated by the first type of enquiry; but that much of the information generally thought necessary in order for consent to be informed is only required if our concern is with the second type of enquiry. For this reason it is neither the case that doctors and researchers should ensure all the information they provide is understood, nor is it the case that their only obligation is to disclose it.