Our paper analyses the competition between right-wing and left-wing populist parties in all those Western European countries where both types of populist parties coexist: France, Germany, Greece, Italy, and the Netherlands. Additional analyses will be carried out to determine the extent to which results can be generalized to those countries in Central and Eastern Europe (CEE) where left and right populits parties compete for the electoral support of voters. Although we know much on the socio-demographic profile of each type of parties separately, comparisons of their social bases have been indirect, in that they rely in different samples of countries. The proper comparison requires to draw inferences from the same sample and hence to compare those cases in which both types of populist parties compete with each other. This is a highly relevant issue not only from a theoretical and substantive point of view, but also from a political one, especially so after the establishment of governing coalitions in Greece and Italy conformed by populist parties with different ideological positions. The celebration of the next European elections in a few months, in which populist parties are expected to obtain a significant share of the votes of EU citizens, lends further significance to our endeavour.