Histories of the role of public health in nation building have revealed the centrality of hygiene to eugenic mechanisms of racial exclusion in the turn-of-the-20th-century United States, yet little scholarship has examined its role in the present day. Through ethnography in a Mexican migrant farmworking community in California's Central Valley, we explore the role of oral-hygiene campaigns in racializing Mexican immigrant parents and shaping the substance of their citizenship. Public health officials perceive migrant farmworkers' children's oral disease as a "stain of backwardness," amplifying Mexican immigrants' status as "aliens." We suggest, however, that the recent concern with Mexican immigrant children's oral health blends classic eugenic concerns in public health with neoliberal concerns regarding different immigrant groups' capacity for self-governance.