Do political preferences reflect individual differences in interpersonal orientations? Are conservatives less other-regarding than liberals? On the basis of past theorising, we hypothesised that, relative to individuals with prosocial orientations, those with individualistic and competitive orientations should be more likely to endorse conservative political preferences and vote for conservative parties. This hypothesis was supported in three independent studies conducted in Italy (Studies 1 and 2) and the Netherlands (Study 3). Consistent with hypotheses, a cross-sectional study revealed that individualists and competitors endorsed stronger conservative political preferences than did prosocials; moreover, this effect was independent of the association between need for structure and conservative political preferences (Study 1). The predicted association of social value orientation and voting was observed in both a four-week (Study 2) and an eight-month (Study 3) longitudinal study. Taken together, the findings provide novel support for the claim that interpersonal orientations, as measured with experimental games rooted in game theory, are important to understanding differences in ideology at the societal level. © 2011 John Wiley & Sons, Ltd.