This study quantifies the effects of stressful weather and elevated air pollution levels on cause-specific mortality in Santiago, Chile, during the austral winters from 1988 to 1996. A temporal synoptic index (TSI) is used to form weather classes and air pollution classes. Prior applications of the TSI have formed classes solely on the basis of weather and may have systematically underestimated the impact of air pollution levels on daily mortality. In Santiago, the attribution of increased mortality risk was found to be largely dependent on the type of class formed (weather or pollution). High-mortality weather classes were associated with cold, dry and high-pressure conditions, while high-mortality pollution classes were associated with elevated NO(2) and PM(10-2.5) concentrations. Cardiovascular disease mortality was more sensitive to weather conditions, and respiratory mortality was more sensitive to pollution levels. Respiratory mortality was most sensitive to stressful conditions at longer lag times (3-6 days), while cardiovascular mortality was most sensitive at shorter lag times (0-2 days). By understanding the relative magnitudes of health risks associated with stressful weather and air pollution conditions we can improve existing air pollution/weather watch systems and better anticipate future, risks associated with global climate change. Copyright (C) 2007 Royal Meteorological Society.