Objective: Case-crossover studies on air pollution and health usually use pollutant concentrations averaged per city as exposure measurements. As part of the PAISA project (Air Pollution and Socioeconomic Inequalities in Asthma), we conducted a case-crossover study testing whether ambient pollution concentrations measured for finer geographic resolution (IRIS neighborhoods, ∼2000 inhabitants, comparable to US Census Block Group) are associated with emergency calls for asthma attacks. Material and Methods: Our study setting is an eastern France conurbation of 190 IRIS, including 450,000 inhabitants. Data on 4683 emergency calls for asthma attacks (georeferenced by IRIS from which the calls were given) were obtained from the 2 emergency and health care networks operating in the conurbation for years 2000 to 2005. Levels of ambient PM10, NO2, SO2 and O3 in each IRIS were modeled on an hourly basis from emission inventories, meteorological data, and pollution measurements of the Local Air Monitoring Association using the deterministic model ADMS-Urban (years 2000–2005). Results: Preliminary analyses adjusting for influenza epidemics, pollen release bursts, holidays, and meteorological factors (relative humidity, pressure, temperature) have shown that, when concentrations were averaged on the day of the event and on the previous one, emergency calls for asthma attacks were positively (although not significantly) associated with 10 μg/m3 increases in PM10 (OR = 1.034; 95% CI = 0.996–1.074), NO2 (OR = 1.023; 95% CI = 0.982–1.065), and SO2 (OR = 1.054; 95% CI = 0.978–1.137). No positive associations were found for more remote lags. Analyses for O3 are underway. Conclusions: Alternative analyses using pollutant concentrations averaged citywide will be presented. This will allow testing whether neighborhood-based exposure measurements are more strongly associated with calls for asthma attacks than city-based ones. Further studies will test the role of neighborhood socioeconomic status as an interaction factor in the observed associations.