Numerous studies concerning European urban regions have recognised a shift from monocentric cities to increasingly polycentric city regions. Fewer studies, however, have addressed such development in northern Europe, at least on an intra-urban scale (as distinct from polycentricity understood as a network of cities). In polycentric cities, functional criss-cross relations are assumed to exist between the nodes of the urban system. The functional role of centres in polycentric city regions is an emerging but still rather a neglected field of research and few studies have empirically examined the existence and significance of such criss-cross relations. In the paper, I intend to examine the polycentric development of the three largest urban regions in Finland between 1980 and 2007. Furthermore, the functional role of the centres in the studied urban regions is analysed. For this purpose, a new method of spatial analysis is introduced where the level of functional polycentricity is measured using detailed commuting data. In the paper, the methodology and empirical results are presented. The findings are reflected against the wider European context and the scalar adjustability of the methodology is discussed.