Recent exposure to general-information facts creates a tendency to claim that the facts had been known prior to their exposure. In Experiment 1, this "illusory knowledge effect" occurred even when participants did not have to demonstrate their knowledge by recalling part of the fact. In Experiment 2, the effect was found for both true and false facts. These findings suggest that the tendency to claim tha recently presented facts had been previously known is caused by their enhanced familiarity. Accounts that would attribute this effect entirely to an underestimation of participants' knowledge of the new facts or to participants' intentional inflation of their prior knowledge states are not supported by these results.