Three experiments tested whether counterfactual events can serve as primes. The evidence supports the hypothesis that counterfactuals prime a mental simulation mind-set that leads people to consider alternatives. Exposure to counterfactual scenarios affected person perception judgments in a later, unrelated task and this effect was distinct from semantic construct priming. Moreover, these effects were dependent on the availability of salient possible outcomes in the person perception task. Direction of the counterfactual comparison, upward or downward, did not moderate any of the effects, providing evidence that the process of thinking counterfactually, and not the content of the counterfactuals, was responsible for the priming effects. These experiments also provide evidence that the effects of mind-set accessibility, similar to semantic construct accessibility, are limited by the applicability of the primes to the later judgments. Implications for the nature of priming effects are discussed.