Since the end of the 2000s, the question of the decline of French medium-sized towns has become central within the scientific and public debate. More specifically, two processes are underlined: the devitalisation of city centres on the one hand, and urban shrinkage on the other hand. The devitalisation of city centres has been studied in several institutional reports. It is characterised by high rates of vacant housing and high street shops vacancies, a fall in visits to the city centre, an impoverishment of residents and population losses. In geography, urban studies and planning, the dynamics of urban shrinkage have been discussed since the 1990s. They comprise a multidimensional urban crisis, triggered and characterised by job and population losses. This paper attempts to explore the relationships between these processes by underlining their similarities and differences with data analysis and multivariate clustering methods. By comparing medium-sized cities with small and large cities, the specificities of urban decline in medium-sized cities are explored. It appears that cities are not homogeneously affected by urban decline. More particularly, a large number of weakened medium-sized cities display a distinctive feature: markers of decline are concentrated in their urban core.