Objective: To investigate long-term clinical effects of fissure sealing in permanent teeth with regard to sealant retention, reduction of occlusal caries, and effect on the increment of smooth surface caries. Method and Materials: The study included 360 children aged 7 to 8 years with caries-free permanent teeth. Children were divided into 4 groups, and fissure sealing was performed as follows: group 1-1 maxillary first molar and 1 mandibular first molar sealed; group 2-all first molars sealed; group 3-all molars and premolars sealed on eruption; group 4-controls, no teeth sealed. Materials used for sealing were Nuva-Seal (Caulk), Concise Brand White Sealant System (3M ESPE), and Concise Enamel Bond System (3M ESPE). Control examinations were performed over 15 years, every 6 months for 2 years and then every 12 months. Results: Complete sealant retention after 15 years was observed in 22.0% of cases, and partial retention in 35.0%. The degree of sealant retention affected the occurrence of occlusal caries in sealed teeth. Reduction in caries after 15 years was 36.0% when all first molars were sealed and 54.0% when all posterior teeth were sealed. Caries developed in 7.4% of teeth with complete sealant retention, in 15.0% of teeth with partial sealant retention, and in 31.0% of teeth with complete loss of sealant. Conclusions: The degree of sealant retention depends on the duration of observation and tooth type. The degree of caries reduction depends on the number of teeth sealed. Mean caries increment was lower in children with sealed teeth than in controls. Keywords: dental caries, occlusal caries, pit and fissure sealant, sealant retention