Peri-urban rural areas are undergoing profound change in many regions, including the northern region of Belgium, Flanders. One driving force is the gradual conversion from an agriculturally based economy to a much more diverse economic base. Re-use of rural buildings by nonagricultural entrepreneurs is a part of this economic diversification. This re-use is changing not only the rural economy but also the social structure and spatial and environmental quality. However, re-use of rural buildings is chronically and severely underestimated. In most cases these activities are prohibited by spatial legislation, which results in their exclusion from census data. Standard methods based on measuring land use change do not measure this transformation either, as these new activities do not necessarily lead to a change in land use. This paper presents a survey method for describing and quantifying this hidden re-use of rural buildings by non-agricultural entrepreneurs. Several datasets were combined in a GIS environment. This led to an inventory which was further refined by confirming the knowledge of local civil officers and local authorities. Field visits provided final confirmation of the data. A case study using this survey method gave profound quantitative insights in the re-use dynamic for the region of Roeselare-Tielt in the north western part of Belgium. In the rural areas of this region, 1015 addresses were detected housing a non-agricultural activity. Further information was gained about the type and the age of the detected activity and the type of building in which these activities are taking place. The most common activities are (building) contractors, trade or commercial companies, landscapers, transport and woodworking companies. Furthermore, 35% of all detected enterprises are located in (former) farm buildings. These results then formed the starting point for individual interviews and focus group discussions on the current policy on this non-agricultural dynamic. Studying the re-use dynamic in the rural areas of the north western part of Belgium (Flanders), provides further knowledge on the economic diversification of rural areas under high urbanisation pressure. The results also illustrate that the current policy lacks both data and efficiency. A clear discrepancy was found between the legal rules, spatial reality and the policy attitude towards the reported illegal non-agricultural economic dynamic. We call for increased awareness of the non-agricultural re-use of rural buildings, given the effect on future spatial planning. 0 2011 Elsevier Ltd. All rights reserved.