The implementation of a school-based mouth-rinsing program in a Long Island, NY, community was described. In this program, children rinse once a week with a neutral 0.2% sodium fluoride solution under the supervision of homeroom teachers. Although the children reside in a fluoride-deficient community (F less than or equal to 0.1 ppm), the baseline dental caries prevalence of a subsample of the group (11 to 13 years old) was similar to that of comparably aged children who were residents of a fluoridated community and from approximately a third to a half lower than that of other fluoride-deficient communities. Despite the initially low caries activity in the study population, there was a 19.9% difference in mean DMFT prevalence scores between the baseline and two-year examination and a 20.3% difference in DMFS scores after two years of rinsing (average of 49 rinses). The greatest difference, 40.0%, was found between proximal surfaces; differences for occlusal and buccolingual surfaces were 19.6% and 15.6%, respectively.