We examine a novel class of conformist preferences that is within the realm of beliefdependent motivations, in that the peers’ expectations about others’ behavior may affect every group-member’s welfare. Similar social-preference motivations (such as guilt aversion) have been inferred from evidence of a belief-behavior correlation, but the issue of causality has been called into question. In examining conformism, we propose a design that verifies the presence of the relevant causality direction while ruling out alternative social-preference motivations. Our data reveal “self-servingly conformist” behavior in that subjects choose to match their strategy to the peers’ expectations when it is in their material interest to do so.