This paper compares the levels of socio-cultural integration of naturalised and non-naturalised immigrants in the Netherlands, France and Germany. Socio-cultural integration is measured by host-country identification, proficiency and use of the host-country language, and interethnic social contacts. To increase cross-national comparability, we focus on immigrants from two rural regions in Turkey who migrated before 1975. Based on the assumption that easily accessible citizenship promotes socio-cultural integration, we test two hypotheses. First, whether naturalised immigrants display higher levels of socio-cultural integration than non-naturalised immigrants. Second, whether immigrants in countries with few preconditions for naturalisation show higher levels of socio-cultural integration. We find that naturalisation is positively associated with socio-cultural integration only in those countries-France and Germany-that have traditionally required a certain degree of cultural assimilation from their new citizens. Regarding country differences, we find that Turkish immigrants in France show higher levels of socio-cultural integration on all four indicators. For host-country identification, they share this position with Dutch Turks. The results show that limited cultural assimilation conditions tied to citizenship may be helpful in promoting socio-cultural integration, but also that the allowance of dual nationality does not have the negative effects that are sometimes ascribed to it. © 2010 Taylor & Francis.