Is it ethically permissible to use deception in psychological experiments? We argue that, provided some requirements are satisfied, it is possible to use deceptive methods without producing significant harm to research participants and without any significant violation of their autonomy. We also argue that methodological deception is at least at the moment the only effective means by which one can acquire morally significant information about certain behavioral tendencies. Individuals in general, and research participants in particular, gain self-knowledge which can help them improve their autonomous decision-making. The community gains collective self-knowledge that, once shared, can play a role in shaping education, informing policies and in general creating a more efficient and just society.