In Europe, urban shrinkage has emerged as a prominent and concerning phenomenon. It is affecting an increasingly large number of cities, particularly small and medium-sized ones. Nonetheless, the dynamics and causes vary at national level. It is a recent process in Spain, although in the 21st century, and especially since the great recession, the number of shrinking medium-sized cities has expanded. This evolution is yet to be sufficiently addressed in the literature, and, in politics and the media, it has been overshadowed by rural depopulation. The aim of this study is to shed light on what is happening in shrinking medium-sized cities, based on the case of Spain. To do so, we combine multiple demographic and socioeconomic variables with depopulation. The correlational analysis reveals a link between depopulation and ageing due to the fall in the potential working population, while births and the population aged below 16 years decreases and that aged over 65 years increases. Additionally, depopulation is correlated with the loss of working population, although no significant correlations can be established between depopulation and the economic variables considered. Drawing on the relationships identified, we established a statistically significant multiple linear regression model. This article represents a novel contribution that may be of practical use for policymakers.