Little information is available on the effect of fluorides on root surface caries in adults. This double-blind clinical study of 810 healthy adults, aged 54 and older, demonstrated decided cariostatic effects of a fluoridated dentifrice containing 1,100 ppm F as sodium fluoride. Statistically significant differences on both coronal (41%) and root surface caries (67%) incidence were produced in the test group and compared with a control dentifrice group during 1 year of study.