Scientific studies have revealed incipient reurbanization in terms of Berg's theory of urban spatial change (cf. BMVBS/BBR: 20; BERG et al.). These spatially different demographic developments impact directly on spatial planning, particularly on social and ecological issues such as gentrification, land use or transport. It is therefore important to consider to what extent reurbanization exists, how it will develop in the future and how it can be assessed from the perspective of sustainable development. Given the lack of empirical evidence regarding reurbanization, its causes and interdependencies and taken into account that the development of local populations becomes increasingly dependent on migration as the German population shrinks, the Institute for Transport Planning and Logistics, Hamburg University of Technology carried out an interdisciplinary case study focusing on the development of intra-regional migration within the city region of Hamburg and its impact on transport development as one of the crucial consequences of intra-regional migration in the past. Primary data were collected concerning the reasons for migration into the city and changes in mobility behaviour. This paper presents the most important aspects of the empirical results on inter-related causes and effects and methodological cognition. Firstly, it discusses experience of the "mixed methods" approach, developed to survey changes in mobility behavior and based on the qualitative method of MAYRING. Secondly, it presents the results of the quantitative analysis of intra-regional migration based on a detailed system of spatial categories. With regard to middle-order-centers of the city region and urban quarters in Hamburg, it reveals considerable change over a ten year period. Thirdly, it highlights the reasons for change of residence from surrounding areas into urban quarters. Due to the preliminary character of the survey, this question only applies to one selected group of these migrants (families). Lastly, it will present selected results from the survey on changes in mobility behaviour in the chosen group, particularly those which have immediate consequences for sustainable planning. BMVBS/BBR: Online Publikation 21/2007 BERG et al.: A Study of Growth and Decline. 1982 MAYRING: Qualitative Inhaltsanalyse: Grundlagen und Techniken. 2003