Segregation may have profound effects when it is paired with an accumulation of inequalities. This is namely the case when ethnic and socioeconomic segregation overlap. Few studies in Europe have, however, addressed the relationship between ethnic and socioeconomic segregation in a comprehensive manner. This paper first aims at investigating the interrelation between ethnic and socioeconomic segregation in Belgium. Second it looks into the role of scale in the relationship between ethnic and socioeconomic segregation. The analyses are based on the newly available geocoded data from the 2011 Belgian census. These data were used to construct individualised neighbourhoods at nine scales with a nearest-neighbours approach for the urban agglomerations of Brussels, Antwerp, and Liege. Ethnic and socioeconomic indicators calculated for these individualised neighbourhoods were then inputted in independent factor analyses for each agglomeration. The results reveal remarkably similar segregation patterns in the three cities. Our analyses give way for three main conclusions: there is an undeniable process of spatial isolation of deprived migrants in Belgium's inner cities; despite the central location of neighbourhoods with high concentration of migrants and poverty, the scope of isolation is considerably high, both in extension and in population density; and macro/national factors such as housing policies and territorial processes seem to shape the segregation patterns in Belgian cities.