Tropospheric ozone is a main component of the “photochemical smog”. Most of the Polish population is exposed to it in concentrations exceeding the WHO Air Quality Guidelines, and its substantial part also to levels exceeding air quality standards legally binding in Poland. Ozone causes development and exacerbation of respiratory diseases. Epidemiological studies also show an increase in the number of hospital admissions and in mortality on days with increased ozone levels. Growing number and quality of large cohort studies indicate also negative health effects of long‑term exposure to ozone, such as increase in asthma incidence and mortality, including that due to cardiovascular diseases. Health burden of ozone exposure is, according to current assessments, markedly lower as compared to the fine particulates health effects. However, growing knowledge on health effects of ozone may, in the near future, enable to significantly increase these estimates, especially that the changes in population exposure are expected to be small.