The objectives of this study were to evaluate systematically the evi-dence of the caries-preventive effect of fissure sealing of occlusal tooth surfaces and to examine factors potentially modifying the effect. The search strategies included electronic databases, reference lists of arti-cles, and selected textbooks. Inclusion criteria were randomized or quasi-randomized clinical trials or controlled clinical trials comparing fissure sealing with no treatment or another preventive treatment in children up to 14 years of age at the start; the outcome measure was caries increment; the diagnostic criteria had been described; and the follow-up time was at least 2 years. Inclusion decisions were taken and grading of the studies was done independently by two of the authors. The main measure of effect was relative risk reduction. Thirteen stud-ies using resin-based or glass ionomer sealant materials were included in the final analysis. The results showed that most studies were per-formed during the 1970s and a single application had been utilized. The relative caries risk reduction pooled estimate of resin-based seal-ants on permanent 1st molars was 33% (relative risk = 0.67; CI = 0.55-0.83). The effect depended on retention of the sealant. In conclu-sion, the review suggests limited evidence that fissure sealing of 1st permanent molars with resin-based materials has a caries-preventive effect. The evidence is incomplete for permanent 2nd molars, premo-lars and primary molars and for glass ionomer cements. Overall, there remains a need for further trials of high quality, particularly in child populations with a low and a high caries risk, respectively.