Women vote less than men in many parts of the world. Whether this gender gap is due to cultural preferences stemming from traditional gender norms or to structural constraints is hard to answer because preferences and beliefs are endogenous to the socioeconomic and institutional environment. To address this problem, we use the so-called epidemiological approach. This approach exploits the portability of culture as a source of identification, by comparing migrants from different cultures of origin but living in similar institutional environments. We study the gender patterns in turnout of immigrants and their children in Norway using administrative register data on voter turnout. We find that gender traditionalism at country of origin is significantly correlated with the gender gap in the first generation, but has no effect in the second generation. Together, our results suggest that early institutional exposure is important for political assimilation.