Scholars have recently stressed two important avenues for the study of cultural diversity and social capital: the role of political integration regimes as well as alternative indicators to generalised trust. This article addresses both. Focusing on Germany, it provides the first study of the relationship between cultural diversity and social capital in a country implementing an ‘assimilationist’ model of integration. As a further innovation, the article contrasts social trust with an alternative, yet often neglected form of social capital, namely norms of reciprocity. Results based on data from the German Socio-Economic Panel (GSOEP) and using multi-level analyses of 97 German regions suggest a negative relationship between cultural diversity and social trust in Germany. Assimilationist policies have not (yet) led to efficient integration of minority groups and a value convergence that could bridge cultural divides. Nevertheless, cultural diversity does not erode the commitment to norms of reciprocity, which may therefore be regarded as an alternative foundation of social cohesion in culturally diverse societies.