The effects of semi-annual and 3.5 yr mean ozone (O3) concentrations on children's forced vital capacity (FVC) and forced expiratory volume in one second (FEV1) were assessed over a study period of 3.5 yrs in 2,153 schoolchildren from 15 study sites in South Western Germany and Lower Austria. Spirometric parameters were assessed twice a year, and differences between consecutive measurements divided by days were considered as a measure of lung growth. Exposure was analysed in four classes, separately for winter and summer (semi-annual mean O3 concentrations 22-30, 30-38, 38-46, 46-54 parts per billion (ppb) in summer and 4-12, 12-20, 20-28, 28-36 ppb in winter). Regression methods for repeated measurements were used, and these revealed a significantly lower FVC (FEV1) increase estimated at -19.2 (-18.5) mL x 100 days(-1) for semi-annual mean O3 exposure in summer between 46 and 54 ppb compared to exposure between 22 and 30 ppb. However, in winter, the estimated difference in FVC (FEV1) was 16.4 (10.9) mL x 100 days(-1) between the semi-annual O3 class 28-36 ppb and the 4-12 ppb class. By means of linear regression the study found that there was no association between growth rates and mean summer O3 for FVC and FEV1 over a 3.5 yr period. The authors conclude that medium-term effects on schoolchildren's lung growth are possibly present, but are in the long-term not detectable for forced vital capacity and forced expiratory volume in one second over a 3.5 yr period due to partial reversibility.