The concept of multiculturalism has been widely used in cross-cultural research to describe positive attitudes towards a culturally plural society and practices that support cultural diversity. To date, attitudes towards multiculturalism among majority and minority group members have been assessed with the same instruments. However, there is little psychometric evidence that these measures operate appropriately in various cultural contexts. The purpose of the present study was to investigate the factor structure of the Multicultural Ideology Scale (MIS; Berry & Kalin, 1995) and test its measurement invariance across different language versions and ethnic groups. The entire sample consisted of 1572 adolescents and adults in Luxembourg, including native majority members (N = 693) and immigrants from diverse ethnic backgrounds (N = 879). Participants were given the option to complete the questionnaire in one of the following languages: English, German or French. The unidimensional model of multicultural ideology did not show an acceptable fit of the data across all language versions of the MIS. Exploratory and confirmatory factorial analyses revealed a two-factor structure, which was partially invariant across two different language versions (English and German). The two factors reflected positive and negative attitudes towards cultural diversity respectively. Subsequent multigroup confirmatory factor analyses supported configural and metric invariance across majority and minority group members. Scalar invariance was not established, indicating that respondents across these two groups conceptualize multiculturalism in different ways. Implications of these findings are discussed together with methodological issues concerning the assessment of measurement invariance.