Objective: To demonstrate the effectiveness of a dental caries prevention program on the primary dentition of Chilean rural children, using fluoridated powdered milk and milk derivatives. Methods: Fluoridated milk and milk-cereal was given to about 1000 children in Codegua, a rural community located in the 6[SUPth] Region of Chile, using the standard National Complementary Feeding Program (PNAC). The daily fluoride dose from fluoridated powdered milk was estimated at 0.25 mg for infants (0-2 years old), 0.5 mg for children aged 2-3 years and 0.75 for children aged 3-6 years. Cross-sectional samples of children aged 3-6 years were taken from Codegua (study community) from 1994 to 1999 and from La Punta (control community) from 1997 and 1999. Results: Significant reductions (72%) were observed in the dmfs indices in the 3-6-year-old groups Codegua, when comparing 1999 with 1994 data. In 1999, children in the study community showed significantly lower dmfs than children in the control community (41%). The proportion of caries-free children in the study community increased after 4 years of program implementation (from 22.0% to 48.4%), Conclusion: Under Chilean rural conditions, fluoridation of powdered milk distributed through the PNAC is an effective caries prevention alternative for areas where water fluoridation might not be feasible. [ABSTRACT FROM AUTHOR]