Objective/Context: This article has two goals. First and foremost, it seeks to demonstrate an increase in class voting during the 2018 presidential elections in Colombia compared to electoral years 2006, 2010, and 2014. Second, the article aims to develop a possible explanation of this phenomenon. We hypothesize that class voting in the 2018 presidential elections increased due to growing ideological polarization between the two presidential candidates, Iván Duque and Gustavo Petro, both in the left-right and the populist-non-populist dimensions. Methodology: We use data from the National Registry of Civil Status and maps of socio-economic stratification to identify electoral results according to social class in five main Colombian urban centres: Bogotá, Medellín, Cali, Barranquilla, and Cartagena. To measure class voting, we develop the Index of Voting Difference (IVD), which identifies the difference in electoral behaviour between two social classes. We also compare the difference between expected and observed voting for each presidential candidate in the upper, middle, and lower classes. Conclusions: There was an evident increase in class voting in the 2018 presidential elections in Colombia compared to those of 2006, 2010, and 2014. Our analysis shows that such a phenomenon could result from an increased ideological polarization between the two principal presidential candidates, both in the left-right and populist-non-populist dimensions. Originality: This is the only article we are aware of that explores levels of class voting across different presidential elections in Colombia and the relationship between ideological polarization and class voting.