The aims of the present study were to provide quantitative data on the impact of air pollution on the health of people living in Tehran city, the most populated city of Iran. The approach proposed by the World Health Organization (WHO) was applied using the AirQ 2.2.3 software developed by the WHO European Centre for Environment and Health, Bilthoven Division. Concentrations of ozone, nitrogen dioxide, sulfur dioxide and particulate matter of aerodynamic diameter ≤ 10 μm (PM₁₀) were used to assess human exposure and health impacts in terms of attributable proportion of the health outcome, annual number of excess cases of mortality for all causes, and cardiovascular and respiratory diseases. The annual average of PM₁₀, SO₂, NO₂ and O₃ in Tehran were 90.58, 89.16, 85 and 68.82 μg/m³, respectively. Considering short-term effects, PM₁₀ had the highest health impact on the 8,700,000 inhabitants of Tehran city, causing an excess of total mortality of 2194 out of 47284 in a year. Sulfur dioxide, nitrogen dioxide and ozone caused about, respectively, 1458, 1050 and 819 excess cases of total mortality. Results indicate that the magnitude of the health impact estimated for the city of Tehran underscores the need for urgent action to reduce the health burden of air pollution.