The aim of this study was to evaluate the impact of urban air pollution, assessed through reliable indicators of exposure, on asthma and allergies in schoolchildren. A validated dispersion model combining data on traffic conditions, topography, meteorology and background pollution was used to relate 3-yrs averaged concentrations of major urban pollutants at the sites of schools to skin prick tests, exercise-induced asthma and reported asthma and allergies in 6,683 children (9-11 yrs) attending 108 schools randomly selected in six French communities. For the 4,907 children who had resided at their current address for the past 3 yrs, asthma (exercise induced, past year and lifetime) was significantly positively associated with benzene, SO(2), particles with a 50% cut-off aerodynamic diameter of 10 microm (PM(10)), nitrogen oxides (NO(x)) and CO. In the same children, eczema (lifetime and past year) was significantly positively associated with benzene, PM(10), NO(2), NO(x) and CO, lifetime allergic rhinitis with PM(10) and sensitisation to pollens with benzene and PM(10). Among the 2,213 children residing at their current address since birth, the associations persisted for lifetime asthma with benzene (adjusted OR per interquartile range (95% CI) 1.3 (1.0-1.9)) and PM(10 )(1.4 (1.0-2.0)), and for sensitisation to pollens with volatile organic compounds (1.3 (1.0-1.9)) and PM(10) (1.2 (1.0-1.9)). Accurately modelled urban air pollution was associated with some measures of childhood asthma and allergies.