This report compares the caries experience rates of 4 groups of 6, 7 and 8 yr. old Evanston children. The 1st, or base line group (1946), had no exposure to fluoridated water. The 2d (1948), 3d (1950) and 4th (1951) groups were exposed to the fluoridated water 12-22 mos., 35-46 mos. and 47-58 mos., respectively, at the time of examination. The ages of the children in group 4 at the time of introduction of NaF to the Evanston water, ranged from 9-55 mos. Regardless of age at the time of fluoridation, the crowns of the deciduous teeth of these children had been calcified. Of the 6 yr. olds examined in 1951 only the deciduous incisor teeth had erupted when NaF was placed in the water. The changes in the deciduous dental caries experience rates for the 1951 group was not considered significant when compared to the 1946 base line group. However, the dental caries experience rate of the permanent teeth of the same group was reduced by 46.4% when compared to the base line rate in 1946.