The aim of the article is to present the process of changes which occurred from the 1970s until 2012 in the areas of urban agglomerations in Poland. In contemporary agglomerations in Poland, their socio-economic function is centralized while land use and building development become progressively decentralized, which results in dynamic growth of the central metropolitan area, and in simultaneous deurbanization of its zone of influence. The described problem is typical of the Warsaw Urban Agglomeration (Warszawski Zespół Miejski, WZM), where the population of the metropolitan zone increases while the importance of the surrounding towns, particularly in their central areas, decreases. The objective of this paper is to present these contemporary trends in the communes of the northern zone of WZM. The analysis involves three towns: Legionowo, Nowy Dwór Mazowiecki, and Zakroczym, and two communes – Jabłonna and Wieliszew. The results are compared with relevant changes occurring in the communes of the Piaseczno district. The examined processes are also confronted with the proposals and arrangements included in planning concepts prepared in different periods for the agglomeration. The escalating suburbanization, characterized by deurbanization visible in spatial planning, affects the effectiveness of newly created building developments and their rank of service centres, and also shows the failure of long-term planning, which is not supported by detailed analysis and research.