The hypothesis is examined that casting a ballot in one election increases the voter's propensity to go to the polls in the future. Voter turnout patterns in the 1972–76 and 1992–96 American National Election Panel Surveys, as well as published experimental research, indicate that the effects of past voter turnout on current voting propensities are sizeable. Moreover, these effects are robust across a wide range of model specifications, including those that take into account the possibility of unobserved factors affecting both past and current turnout. We conclude by discussing the implications of consuetude for political and social behaviour.