This work aims to deepen recent studies on the impact of air pollution on human health in Latin American cities. A time series study has been performed comparing the mortality attributable to atmospheric carbon monoxide (CO) and nitrogen oxides (NOx) in Santiago (Chile) and Buenos Aires (Argentina). Pollution, meteorological and mortality data have been integrated in a general additive model (GAM) to establish the correlation between pollutant concentration levels and daily death counts. The analysis includes other variables such as gender, age and causes of death for each city with the result that both cities show increased deaths that can be attributed to an increase in CO and NOx levels. The impact is higher for Santiago's populations, for all the studied groups. This may be related to previous exposure to high pollution levels or to the co–presence of other pollutants not accounted for in this study.