Polycentrism is becoming one of the dominant structures in contemporary metropolises. Concentrated decentralization and the integration of formerly independent cities by the reduction of travel time are behind of such a process. In this paper, the spatial structure of the seven biggest metro areas in Spain is depicted. By analysing employment density and travel-to-work data the polycentric structure of them is detected at the time that the functional borders are delimited. Results suggest a very heterogeneous image where Barcelona, Valencia and Bilbao emerge as the most polycentric areas at the time that Madrid, Seville and Zaragoza have a structure more orientated towards monocentrism, Málaga is an exception since having few subcentres, their share in employment concentration is important. Clearly a correlation between polycentrism and complexity of the relations among subcentre emerges.