In this paper, the regional Index of Sustainable Economic Welfare (ISEW) is compiled for Flanders for the period 1990–2009. The ISEW is a measure of economic welfare in that it measures the contribution of a country’s or region’s economy to the overall level of well-being of its citizens. It does so by comparing the benefits and the costs of economic activities rather than simply looking at the market value of all final goods and services produced in an economy (Gross Domestic Product-GDP). The ISEW for Flanders shows that the per capita level of sustainable economic welfare in the region decreased between 1990 and 2009. The drop in the ISEW/capita is caused by a deterioration of the net international investment position of Belgium (which is divided over the different regions in the country on a per capita basis) and by an increase in the income inequalities in Flanders. To a lesser extent, the increase of the environmental costs (climate change and the use of non-renewable energy resources) also contributed to the decrease in the ISEW per capita. In the last four years of the study period, the level of sustainable economic welfare in the Flemish region started to rise again, even in 2008 and 2009 during the economic recession.