The objective of the present study was to determine the caries experience of schoolchildren aged 7-12 years from the Southeast area of Sao Paulo State, Brazil, in 1998, according to town size and fluoridation status. Data for this cross-sectional study were based on the data bank from the Epidemiological Survey of Sao Paulo State provided by the State Health Department. After stratification by fluoridation status and town size, 29 towns were randomly selected to represent the Southeast area of Sao Paulo State, Brazil, and a total of 13,480 schoolchildren were randomly selected for this study. Calibrated dentists performed clinical examinations according to the WHO criteria. Caries experience and prevalence were significantly lower in fluoridated areas (1.9 DMTT, 2.1 dmft, 20% caries free) than in non-fluoridated areas (2.4 DMTT, 2.4 dmft, 13% caries free). According to town size, DMTT and caries prevalence were significantly higher in small towns (2.3 DMTT, 13% caries free), followed by medium-sized (2.1 DMTT, 17% caries free) and large cities (1.6 DMTT, 27% caries free). Among 12-year-old children, caries prevalence was predominantly moderate or high in small and medium-sized municipalities, whereas in large cities it was moderate or low. The results suggest that water fluoridation is an essential public health measure and that town size may affect caries distribution in the Southeast area of Sao Paulo State.623124128