Multiculturalism, or the belief that racial and ethnic differences should be acknowledged and appreciated, has been met with both positive reactions (e.g., decreased prejudice) and negative reactions (e.g., perceptions of threat) from dominant group members. The present research proposes that multiculturalism can either positively or negatively influence White Americans' intergroup attitudes depending on their degree of ethnic identification. In Studies 1 and 2, White Americans primed with multiculturalism exhibited higher social dominance orientation (Study 1) and greater prejudice (Study 2), especially when they identified strongly with their ethnicity. In Study 3, perceptions of threat to group values were found to mediate the relation between multiculturalism, ethnic identification, and prejudice among White Americans. The results are discussed in terms of their implications for threat perceptions, ethnic identification, and conceptions of diversity.