OBJECTIVE This study assessed the treatment and posttreatment effects of a school-based, fluoride mouthrinse regimen. METHODS Children in a nonfluoridated community in Japan participated in a daily rinse program using a 0.05 percent NaF solution in nursery and primary schools, and a weekly rinse with 0.2 percent NaF in junior high school. Students were examined at least annually for dental caries and dental treatment was provided in a public dental clinic through the ninth grade. Incipient carious lesions with no cavitation were not restored. RESULTS The percent of children in grades one through nine (6-14 years of age) with caries-free permanent teeth increased from 13.4 percent in 1974 to 73.0 percent in 1991, while the mean DMFT decreased by 86 percent during this period. For 12-year-olds, mean DMFT scores declined to about one tooth per child after 1982. For adults 20 years of age, there was a 64 percent difference in DMFS between the treatment group who started the rinse regimen at 4 years of age and continued for 11 years, and the controls who lived in different districts and did not participate in a fluoride rinse regimen. CONCLUSIONS Children who began rinsing at 4 or 5 years of age benefited the most from the program. The program was inexpensive, simple to implement and well accepted by families and teachers. The conservative treatment policy in the public clinic likely contributed to the benefits derived by participants.