OBJECTIVES Severe air pollution episodes were recorded during the 1980s and early 1990s in the Czech Republic as a result of widespread combustion of brown coal. A population-based retrospective study investigated the relationship between air pollution and daily mortality in six highly polluted areas of the Czech Republic during smog episodes in 1982, 1985, 1987, and 1993. METHODS Total daily mortality, mortality by gender and age, cardiovascular mortality, respiratory mortality, data on weekly incidence of acute respiratory diseases and daily mean concentrations of sulphur dioxide and suspended particulate matter were used in the model. The effects of smog on daily mortality were estimated by multiple linear regression analysis. RESULTS Significant increases in mortality were observed for the 1982 and 1987 episodes (6% and 9%). In 1982, mortality was significantly associated with mean concentration of sulphur dioxide (SO2) of the current and the preceding days and with the 4-day moving average. In the 1985 episode a significant increase in respiratory mortality in men and in both genders together, lagging by 2 and 3 days, was detected. During the 1987 episode significant associations of total daily mortality, mortality in persons over 65 years of age and mortality from cardiovascular or respiratory diseases with 4-day moving average of both pollutants were found. For the 1993 episode a significant association between mortality in women under 65, lagging by 3 days, and mean concentration of suspended particulate matter (SPM) was observed. CONCLUSIONS Most of the results are consistent with other studies aimed at episodic air pollution during the 1950s and 1960s in Western Europe and the USA, in which outdoor air pollution was shown to be a significant predictor of mortality. However, non-significant or opposite associations between air pollution and mortality indicate that other factors may also play an important role. A stronger effect on men under 65 years of age, suggested by a previous Czech study was not confirmed.