The low caries experience of children who consume water containing approxi mately 1 ppm of fluoride throughout childhood persists during adulthood. The teeth of subjects from Aurora (1.2 ppm of naturally occurring fluoride) and Rock ford (0.1 ppm of fluoride) , Illinois, aged 20 to 59 years were examined clinically and roentgenographically. Aurora resi dents had an average of 12 D M F teeth and 27 D M F surfaces, whereas Rockford residents had 19 D M F teeth and 48 D M F surfaces. Although roentgenograms raised the average D M F count over that deter mined clinically for residents of both cities, they did not alter significantly the relative differences between the groups.