Objective: The aim of this study, conducted in 132 randomly selected children, was to evaluate the retention of a fluoride-containing sealant on primary and permanent teeth. Method and materials: In autumn 1995, a total of 195 primary molars in 36 children aged 4.5 years on average and 391 permanent premolars and molars in 96 children aged 10.5 years on average were sealed with Helioseal-F. The manufacturer's instructions were followed closely. The teeth were cleaned with a slurry of pumice and a rotating brush, isolated with cotton rolls, dried with air, etched for 60 seconds with an etching gel (37% phosphoric acid), rinsed with an air-water combination spray, and dried. Sealant was applied with a cannula and polymerized for 60 seconds. A saliva ejector was used throughout the procedure. Sealant retention was checked 3 years after placement. Results: In the primary molars, full retention was found in 95.04%, partial retention in 3.12%, and loss of the sealant in 1.84% of the treated teeth. In the permanent molars, the corresponding rates were 95.81%, 2.83%, and 1.36%, respectively. Conclusion: Very good sealant retention was found 3 years after placement. The observed difference in retention between primary and permanent molars was not statistically significant.