In recent years, an old challenge to informed consent has been rediscovered: the challenge of ignorance. Several authors argue that due to the presence of irreducible ignorance in certain treatments, giving informed consent to these treatments is not possible. The present paper examines in what ways ignorance is believed to prevent informed consent and which treatments are affected by that. At this, it becomes clear that if the challenge of ignorance truly holds, it poses a major problem to informed consent. (...) The paper argues, however, that from both an empirical and a theoretical point of view, it is not convincing that ignorance prevents informed consent. Still, it seems important that the presence of irreducible ignorance is openly discussed during the informed consent process. (shrink)