Abstract How does military conscription influence mass opinion on foreign affairs? Is gender relevant for the impact compulsory service has on public opinion? Leveraging South Korea's mandatory military service for men and fluctuations in inter-Korea relations from 2003 to 2018, we assess conscription's impact on South Korean opinions of North Korea. We rely on the random nature of a child's gender, given the number of children in a family, to infer the effect of conscription on the views of parents via a “son effect." While the gender and foreign policy opinion literature suggests that female aversion to the costs of conflict can result in positive views toward an adversary, we find that the high costs of conscription result in mothers of sons subject to military service holding more negative and hostile perceptions of North Korea compared to women with no sons as well as men. We do not find such differences between fathers of sons and men without sons.