The expansion of middle-income sectors has, in recent years, drawn the attention of academia, international organizations, and governments. However, more recently, several studies have pointed to the vulnerability of these sectors. Based on household surveys, this paper analyzes the evolution of the middle classes in Uruguay in recent decades (1993-2016) using two complementary measures: one based on income and the other on occupation. The results suggest that the change in income levels that characterized the period did not result in a change in the structure of employment and human capital, and they alert about the vulnerability of the middle classes.