This report describes the first-ever multicity study to estimate the effect of short-term exposures to particulate matter (PM10) and to ozone on mortality in nine Latin American cities. Led by Dr. Isabelle Romieu in Mexico, in collaboration with Dr. Nelson Gouveia in Brazil and Dr. Luis Cifuentes in Chile, the researchers evaluated mortality from all causes and in different age groups, using a common analytic framework. They analyzed mortality in each city and the region as a whole, and explored two pollutant models in individual cities. They also used two meta-analytic statistical techniques to further analyze the effects from individual cities.