Urban sprawl is widely considered to be a major issue for the functioning of urban areas, threatening long-term sustainability and affecting the quality of living. The aim of this research is to develop a methodology for assessing the negative effects of uncontrolled suburbanization in metropolitan areas through a multicriterial approach. Based on the existing body of knowledge, we have defined a set of indicators for assessing the impact of suburbanization, covering themes such as land use, water, biodiversity and economy or social issues. A questionnaire was applied to experts in the field in order to find out the final set of indicators and their perceived importance. The product of our research is an urban sprawl restrictiveness index at the local level, tested on five of the most dynamic metropolitan areas in Romania. The results highlight the concentration of negative effects of urban sprawl in the areas most accessible from the city core, where additional in-depth analyses were performed for validation. This study thus proposes a novel method for assessing the negative impacts of urban sprawl. The index could be used in other comparative studies at the national or international level while also aiding policymakers in better managing metropolitan areas.