In the fall of 1975, 1,915 children in grades K through eight began a school-based program of supervised weekly rinsing with 0.2 percent aqueous solution of sodium fluoride in an unfluoridated community in the Finger Lakes area of upstate New York. At baseline and annually thereafter, a random sample of children in grades K through 11 received clinical dental caries examinations. The prevalence of dental caries by grade at each of the follow-up dental examinations was compared to the grade-specific prevalence of dental caries at baseline. Overall, there was a decline of 57.8 percent in prevalence of caries in permanent teeth after seven years of rinsing. Among children in grades K through five, there was a decline of 35.4 percent in the prevalence of caries in primary teeth during the same time period. Tenth and eleventh grade children, after not rinsing for one and two years, respectively, continued to show the same trend toward lower caries prevalence as active rinsers. Caries prevalence among seventh and eighth graders after seven years of rinsing was not significantly different from caries prevalence among seventh and eighth grade lifetime residents of a nearby fluoridated community. A decline in the prevalence of caries in primary teeth among kindergartners prior to rinsing suggests that factors in addition to the mouthrinse program may have contributed to the decline in caries prevalence.