This study assessed the association between school absenteeism and respirable particulate pollution (PM10) in Utah Valley for the six school years of 1985 to 1990. Weekly absenteeism data from the Provo School District and daily data from a single elementary school in the Alpine School District were analyzed for kindergarten through sixth grade. PM10 concentrations during the study period averaged approximately 50 micrograms/m3 with the 24-hr maximum equal to 365 micrograms/m3. Absenteeism was regressed on PM10 pollution levels, temperature, snowfall, and variables indicating day of week, month of school year, and days preceding and following holidays and extended weekends. Estimated associations between absenteeism and PM10 pollution in both data sets were positive, statistically significant (P less than 0.01), and robust to different model specifications. PM10 effects persisted for up to 3 or 4 weeks. Regression results from both data sets indicated that an increase in 28-day moving average PM10 equal to 100 micrograms/m3 was associated with an increase in the absence rate equal to approximately two percentage points, or an increase in overall absences equal to approximately 40%. Similar relationships were observed for all grade levels, although the response of absences to air pollution was generally greater for grades 1-3 compared with grades 4-6. Associations between absenteeism and PM10 pollution were observed even for levels below 150 micrograms/m3.