Nearly all children who attend elementary school (grades K through 6) in a rural community have participated since 1972 in a school-based caries preventive program consisting of daily ingestion of a 1-mg fluoride tablet and weekly rinsing with a 0.2% sodium fluoride solution. 3they also regularly receive toothbrushes and a fluoride dentifrice for use at home. Examinations conducted after four years showed that the prevalence of dental caries among continuous participants, 7 through 12 years of age, was reduced by 35% compared with baseline findings; mean DMFS scores in 1972 and 1976 were 5.39 and 3.49, respectively. The preventive program inhibited decay in all three types of surfaces: approximal surfaces received about twice the relative protection against decay (70%) as buccolingual surfaces (34%) and more than three times as much as occlusal surfaces (22%). A comparison of estimates of four-year increments of decay taken from cross-sectional data at the baseline and actual increments from the 1972 and 1976 examinations showed that, for children ages 6 through 15, the incremental DMFS score was 41% lower during the period of the program than before its initiation. Findings in older children (ages 13 through 15) in 1976 who had stopped participation when they left elementary school at about age 12 showed evidence of strong posttreatment effects--as great as 31% fewer DMFS for 14-year-old children.