This paper focuses on a neglected-horizontal-dimension of social stratification. It examines the patterns of social differentiation in the Visegrád countries (the Czech Republic, Hungary, Poland, and Slovakia) and attempts to assess changes in the social structure at the subnational level. Social structure changes are explained within the context of broader socioeconomic development. The main analyses performed in this study are based on EU-SILC micro-data covering 2006-2016 and offer a comprehensive perspective on the patterns of social-stratification development at the regional level utilising three dimensions: social class (proxied by the European Social-Economic Classification), highest attained education level, and income. The results indicate different trajectories in social differentiation across the four countries, although some of the patterns identified are similar. The results indicate that the working class is shrinking and the salariat is growing, and that there are declining shares of people with at most primary or secondary education and increasing numbers with tertiary education. Income inequalities remained relatively stable over the observed period across the Czech and Slovak regions, but fluctuated in Hungarian regions, and the initially greater income inequalities in Polish regions have tended to decline over time. The findings suggest that the least favourable patterns in the development of regional social differentiation are found in the Hungarian regions.