The purpose of the study was to evaluate the caries preventive effect and cost of an intensive application of Duraphat varnish, added to the regular preventive program for 11-15-yr-old children in a Swedish Dental Community Clinic. In 1987, the 134 11-yr-old children in Floda were divided into two groups, every second child to each. Children with fixed orthodontic appliances were excluded. The test group received three applications of Duraphat varnish during 1 week, once a year, by a dental nurse. The control group received one application at the annual check-up. Both groups were included in the regular preventive program at the clinic. The total time cost for the clinic was estimated and used to calculate the cost per hour for dentists and nurses. The caries increment and progression were estimated both by routine diagnosis and by a careful study of radiographs taken at the beginning and end of the study period. There was a small caries increment and progression in the test group as compared to the control group. The difference was statistically significant for all aspects studied. The costs were about the same in both groups but more time was used in the test group. The administrative effort for the staff was considerable for the intensive Duraphat application.