The caries experience of grade 6 Canadian schoolchildren was examined related to length of residence in non-fluoridated Camrose (0.23 ppm) and adjacent fluoridated Wetaskiwin (1.08 ppm). The mean age was 11.94 +/- 0.65 years, 115 being examined in Camrose and 89 in Wetaskiwin. The mean DMFT and DMFS values were similar in both the non-fluoridated and fluoridated communities with DMFT of 2.39 and 2.65 and DMFS of 3.40 and 3.54, respectively. When a minimum 5-year residency requirement was imposed, the data changed, showing for those children with 5-year residency DMFT values of 2.43 and 2.26 and DMFS values of 3.35 and 2.79, respectively, for non-fluoridated Camrose and fluoridated Wetaskiwin. Although the fluoridated community had 17% less surfaces with caries, differences between the fluoridated and non-fluoridated communities were not statistically significant. Within the fluoridated community, differences in DMFT and DMFS between children resident less than 5 and greater than 5 years were statistically significant (DMFT p less than 0.05; DMFS p less than 0.01). When comparing regions where adjacent communities exist, with and without water fluoridation, and in making decisions on fluoride supplementation levels for children who have changed residency to such communities, it is important that this type of information is taken into account.