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Brazilian cities host 86% of the country's population and have been more intensely hit by rising temperatures than the average of cities across the world over the last century. Nevertheless, assessments of the vulnerability of Brazilian urban dwellers to urban heat islands (UHI) are scarce. In this study, we take advantage of the availability of high-resolution data to calculate the heat stress vulnerability and risk indexes (HSVI and HSRI, respectively) for people inhabiting six Brazilian metropolitan areasManaus, Natal, Vitoria, SAo Paulo, Curitiba, and Porto Alegre. The indexes are calculated by mathematically relating indicators of exposure (distribution of >65-year-old elderly people), sensitivity/adaptive capacity (human development index, HDI), and hazard (surface temperature). The resulting HSVI maps reflect the socioeconomic (HDI) differences found among the studied cities, with the most vulnerable people located in the poorest neighborhoods in Manaus (0.720) and Natal (0.733), distributed among lower- and mid-class zones in SAo Paulo (0.794) and Vitoria (0.772), or invariably located in the wealthy zones of Curitiba (0.783) and Porto Alegre (0.762). Two distinct patterns are identified for the HSRI: in SAo Paulo, Vitoria, Curitiba, and Porto Alegre, high and very high risks are found in the wealthy zones of the cities, whereas in Natal and Manaus, high and very high risks are encountered in the poorly developed city zones, a result that was strongly driven by the UHI pattern. Better communication of heat stress risk and the improvement of city greenness should be the focus of near-term adaptation strategies for the mapped vulnerable population.