Whether two people are presented as similar or different may have a strong impact on the outcome of their comparison. In the present research, we examined the counterintuitive hypothesis that activating dissimilarity increases the perception of similarities between people, in other words increases perceived feature overlap, during the comparison process. We investigated this prediction by asking people to judge the perceived similarity between two faces with a suboptimally related or unrelated morph inserted in between (to influence joint categorization), and with similar or different facial expressions (to vary the salience of similar or different features). The results confirmed our expectations: In the similarity (joint categorization) condition, two faces that differed in expression were perceived as more dissimilar than faces with the same expression. More important for our prediction, in the dissimilarity condition two faces with different expressions were no longer perceived as more dissimilar than two faces with the same expression. We discuss implications of these findings for the mechanisms underlying comparisons between people. Copyright © 2007 John Wiley & Sons, Ltd.