This study examined reactions to minority and majority positions that were either stable or reversed through group conversion that transformed opponents (supporters) of the minority (majority) into supporters (opponents) or through group expansion that brought new supporters (opponents) for the minority (majority) into the group. Minorities who became majorities through group expansion, compared with those who changed through group conversion, perceived their supporters and the overall group as significantly more similar to the self, and had significantly higher expectations for future positive interactions within the group. Perception of similarity with the supporters mediated the effect of the experimental conditions on perception of the overall group-self similarity. Implications of changes through conversion and expansion for the functioning of social groups are discussed.