Ciudad Juarez, Chihuahua, is home to the U.S.-Mexico border's largest maquiladora labor force, and also its worst air pollution. We marshal two types of evidence to examine the link between maquiladoras and air pollution in Ciudad Juarez, and in its sister city, El Paso, Texas. First, we use a publicly available sector-level emissions inventory for Ciudad Juarez to determine the importance of all industrial facilities (including maquiladoras) as a source of air pollution. Second, we use original plant-level data from two sample maquiladoras to better understand the impacts of maquiladora air pollution on human health. We use a series of computational models to estimate health damages attributable to air pollution from these plants, we compare these damages to estimates of damages from non-maquiladora industrial polluters, and we use regression analysis to determine whether the poor suffer disproportionately from maquiladora air pollution. We find that air pollution from maquiladoras has serious consequences for human health, including respiratory disease and premature mortality. However, maquiladoras are clearly not the leading cause of air pollution in Ciudad Juarez and El Paso. Moreover, most maquiladoras are probably less important sources of dangerous air pollution than at least one notoriously polluting Mexican-owned industry. Finally, we find no evidence to suggest that maquiladora air pollution affects the poor disproportionately.