Emergency room visits for respiratory complaints, considered an indicator of deterioration of respiratory health, have been positively correlated to traffic-related air pollution. This is an ecological study to evaluate the association between daily levels of urban air pollutants and emergency visits for respiratory complaints, in children and the elderly residing in Pisa, Italy. Daily records of emergency department visits for respiratory complaints were selected from computerized registries, and paper medical reports were identified. Pollutant daily means were computed from hourly values obtained from the public network. Poisson regression, allowing for overdispersion and autocorrelation, was used to evaluate the percent change in daily visits associated with variations of air pollution measures. Among children, an increase in emergency visits of 10% (95% CL: 2.3; 18.2) was associated with a 10-microg/m3 increase in PM10 concentrations of the previous day and an increase of 11.8% (95% CL:1.4; 23.3) was associated with an analogous increment of NO2 during the 2 previous days. Among elderly the same increment of PM10 level during the 2 previous days was correlated with a 8.5% (95% CL: 1.5; 16.1) increase in the risk of recurring emergency department visits for respiratory complaints; this risk increased to 26.5% (95% CL: 3.4; 54.8) if the daily level of CO over the 4 previous days increased by 1 mg/m3. Evidence of morbidity related to short- and long-term air pollution exposures provided in this small study and larger studies conducted in other countries suggests the need for actions to improve air quality in any urban context.