The unequal division of cognitive labor within households, and its potential association with mental load and stress, has gained substantial interest in recent public and scholarly discussions. We aim to deepen this debate theoretically and empirically. First, going beyond the question of whether the division of cognitive labor is gendered, we connect cognitive household labor with existing stress theories and ask whether men and women typically perform cognitive labor tasks that involve different levels of stress. We then discuss whether women perform these stressful tasks more often, making them more prone to higher levels of family–work conflict. Second, we test the association between the division of cognitive labor and family–work conflict empirically using large-scale survey data from 10 European countries within the Generations & Gender Programme (GGP). Results based on logistic regressions confirm that a high share of cognitive labor increases women’s family–work conflict, but not men’s. We discuss future directions in the conceptualization and measurement of cognitive labor in the household and its implications for mental load. Through its contributions, this paper lays the foundations for a comprehensive understanding of the implications of an unequal division of cognitive labor in the household for gender inequality.