Against a backdrop of extreme racial health inequality, the 1918 influenza pandemic produced strikingly small ratios of nonwhite to white influenza and pneumonia mortality in United States cities. We provide the most complete account to date of these racial disparities, showing that, across U.S. cities, they were almost uniformly small. Linking data from multiple sources, we examine potential explanations for this result, including [a] city-level socio-demographic factors like segregation, [b] implementation of non-pharmaceutical interventions, [c] racial differences in exposure to the milder spring 1918 “herald wave,” and [d] racial differences in early-life influenza exposures, resulting in differential immunological vulnerability to the 1918 flu. While we find little evidence for the first three explanations, we offer suggestive evidence that racial variation in childhood exposure to the 1889-1892 influenza pandemic may have shrunk racial disparities in 1918. We also highlight the possibility that differential behavioral responses to the herald wave may have protected nonwhite urban populations. By providing a comprehensive description and examination of racial inequality in mortality during the 1918 pandemic, we provide a framework for understanding disparities in infectious disease mortality that considers interactions between the natural histories of particular microbial agents and the social histories of those they infect.