It is sometimes argued that autonomous decision-making requires that the decision-maker’s desires are authentic, i.e., “genuine,” “truly her own,” “not out of character,” or similar. In this article, it is argued that a method to reliably determine the authenticity (or inauthenticity) of a desire cannot be developed. A taxonomy of characteristics displayed by different theories of authenticity is introduced and applied to evaluate such theories categorically, in contrast to the prior approach of treating them individually. The conclusion is drawn that, in practice, the authenticity of desires cannot be reliably determined. It is suggested that authenticity should therefore not be employed in informed consent practices in healthcare.