Objective: Fluoride is the most important factor in the decline of caries in children and adolescents. The aim of this observational study, begun in 2000, was to assess the effect of semiannual topical fluoride application in schoolchildren. Method and Materials: Due to limited resources, only 334 of all first and second grade schoolchildren (6 to 8 years of age, 0.32 ± 1.02 decayed/missing/filled surface [DMFS], schools randomly selected) in Greifswald received a semiannual application of elmex fluid, while the remaining 442 children served as the control group (0.36 ± 1.15 DMFS). In 2002 and 2004, 230 and 349 of these children were re-examined according to WHO criteria by one calibrated examiner (DMFT/S). The parents filled out questionnaires on additional fluoride use, which was summarized as fluoride scores. In the dropout analysis, a selection bias among the dropout, fluoride, and control group regarding age, baseline caries prevalence, additional fluoride use, and sealants was excluded. Results: During the entire study, no adverse effects were recorded with the use of elmex fluid. The caries increment was almost identical in the intervention and control groups (0.81 ± 1.74 and 0.78 ± 1.81 DMFS) with 72% and 69% of the children, respectively, showing no caries increment. The effect of only two applications of elmex fluid might have been overridden by the high background fluoride use. The participants had high mean values of the fluoride scores, reflecting the regular use of fluoride toothpaste and additional fluoride sources, without a polarization within the sample (intervention, 1.40 ± 0.60; control, 1.33 ± 0.60). Conclusion: Further studies should examine the effect of semiannual topical fluoride applications after caries decline. Keywords: caries, efficacy, fluoride, prevention, topical fluoride