Previous work has shown there are robust differences in how North Americans and East Asians form impressions of people. The present research examines whether the tendency to weigh initial information more heavily—the primacy effect—may be another component of these cultural differences. Specifically, we tested whether Americans would be more likely to use first impressions to guide person perception, compared to Japanese participants. In this experiment, participants read a vignette that described a target person's behaviour, then rated the target's personality. Before reading the vignette, some trait information was given to create an expectation about the target's personality. The data revealed that Americans used this initial information to guide their judgments of the target, whereas the Japanese sample based their judgments on all the information more evenly. Thus, Americans showed a stronger primacy effect in their impression formation than Japanese participants, who engaged in more data-driven processing.