This article compares three sets of European main and secondary cities with the aim of verifying whether similar patterns exist in their structural and socio-economic contrasts at the level of the urban region. This is important because some literature suggests fundamental differences between the two types of urban region that should be made visible. A geo-demographic analysis indeed reveals similar contrasts between capital cities and secondary cities, mainly in terms of distribution and incidence of different socio-economic groups. Exploiting these differences contributes both to the typing of the two types of city and to the study of the different forms of functional and institutional integration of the urban region.