Evaluating social others requires processing complex information. Nevertheless, we can rapidly form an opinion of an individual during an initial encounter. Moreover, people can vary in these opinions, even though the same information is provided. We investigated the brain mechanisms that give rise to the impressions that are formed on meeting a new person. Neuroimaging revealed that responses in the amygdala and the posterior cingulate cortex (PCC) were stronger while encoding social information that was consistent, relative to inconsistent, with subsequent evaluations. In addition, these responses scaled parametrically with the strength of evaluations. These findings provide evidence for encoding differences on the basis of subsequent evaluations, suggesting that the amygdala and PCC are important for forming first impressions.