In order to investigate the relation between air pollution and child morbidity in air pollution Sa ˜o Paulo, a time-series study was carried out. Daily records of hospital admispediatric hospital admissions sions for children under 13 years old were obtained at the Health State Secretary, respiratory diseases covering 112 hospitals in the period from October 1992 to October 1993. Daily ecological study levels of PM 10 , ozone, SO 2 , CO and NO 2 were obtained from the environmental time-series state agency (CETESB), while both CETESB and the Institute of Astronomy and Geophysics (IAG) of the University of Sa ˜o Paulo provided daily measures of temperature and relative humidity. Daily counts of child respiratory admissions (RESP) were considered as the dependent variable of pollutants in regression models, controlled for months of the year, days of the week, weather factors, and the daily number of non respiratory admissions (NORESP). PM 10 and ozone were the pollutants that exhibited the most robust association with RESP. The mean levels of PM 10 observed during the period of study (70 g m ؊3 ) were associated with an increase of 12% in RESP. The association between air pollution and RESP was significant within a time lag between 1 to 7 days and was dosedependent. This result indicates that air pollution represents a significant pediatric health problem in Sa ˜o Paulo.