This paper deals with the electoral and political consequences of urban region formation. The electoral geography of new political parties differs substantially from that of traditional ones. New parties are mainly successful in different parts of urban regions. The declining traditional parties have rather a regional pattern, although some of them show new spatial patterns too. These developments are interpreted in the context of the cleavage theory, in which old and new cleavages are linked with a different spatiality. Following the Anglo-Saxon literature an increasing process of polarisation is hypothesised between the welfare state orientated city and a neo-conservative and neo-liberal suburban fringe. This article examines and proofs the existence of these processes in the urban region of Brussels by means of individual-level and ecological electoral data.