This paper challenges recent views of the sociospatial transformations of inner-city neighbourhoods as ‘reurbanisation’, for, it is argued, such views tend to divorce the demographic dimensions of the processes at play from their contrasted social class meanings and implications. In addition, it argues that the ongoing demographic diversification of inner cities in the Western world do not stand for the obsolescence of gentrification as a key concept for understanding sociospatial transformations in these places, but rather that this trend alerts to a need to complement existing interpretations of gentrification with new insights into its demographic underpinnings. This point is illustrated via an exploration of the implications of contemporary changes in transition to adulthood for urban sociospatial structures and housing market dynamics in Brussels. Findings stress that the rapid rise of middle-class young adults in non-family households in Brussels' inner neighbourhoods brings about the reinvestment of the existing private rental market, fuelling in turn a process of rental gentrification. Such process exacerbates the competition for residential space in the city, being strongly detrimental to low-income, working-class households. The paper concludes that notwithstanding all local specifics, everywhere at stake is the need to keep a clear sense of the multiple social class stratifications of demographic change in inner neighbourhoods. Copyright © 2009 John Wiley & Sons, Ltd.