A developmental study is presented in which participants must detect the Thatcher illusion in order to match unfamiliar faces on identity. 114 participants between 6 and 67 years of age completed a matching task whereby face pairs were presented upright or under inversion. At all ages, participants were more accurate matching upright than inverted faces. In an altered version of the Thatcher task, where only the eyes or mouth were inverted, all participants were more accurate and faster to detect eye manipulations than mouth manipulations. The results are discussed in terms of the developmental significance of face inversion, the Thatcher illusion, and the salience for protection from the Thatcher illusion.