Data sources: Cochrane Oral Health Group's Trials Register, the Cochrane Central Register of Controlled Trials (CENTRAL), Medline, Embase, CINAHL, LILACS, BBO, Proquest Dissertations and Theses, Web of Science Conference Proceedings, ClinicalTrials.gov and the WHO International Clinical Trials Registry Platform. Study selection: Randomised or quasi-randomised controlled trials where blind outcome assessment was stated or indicated, comparing fluoride mouthrinse with placebo or no treatment in children up to 16 years of age with a duration of at least 12 months. Data extraction and synthesis: A least two reviewers independently selected studies, abstracted data and assessed risk of bias. Results: Thirty-seven trials involving 15,813 children and adolescents were included. Supervised rinsing in schools was tested in all trials. Twenty-eight studies were at high risk of bias, nine at unclear risk. Thirty-five trials (15,305 participants) contributed data on permanent tooth surface for meta-analysis and found a prevented fraction for D(M)FS = 27%(95%CI 23% to 30%; I2 = 42%) (moderate quality evidence). Meta-regression showed no significant association between estimates of D(M)FS with baseline caries severity, background exposure to fluorides, rinsing frequency or fluoride concentration. The pooled estimate of prevented fraction from 13 studies for D(M)FT = 23% (95%CI, 18% to 29%; I2 = 54%).There was limited information on possible adverse effects or acceptability of the treatment regimen in the included trials. Conclusions: This review found that supervised regular use of fluoride mouthrinse by children and adolescents is associated with a large reduction in caries increment in permanent teeth. We are moderately certain of the size of the effect. Most of the evidence evaluated use of fluoride mouthrinse supervised in a school setting, but the findings may be applicable to children in other settings with supervised or unsupervised rinsing, although the size of the caries-preventive effect is less clear. Any future research on fluoride mouthrinses should focus on head-to-head comparisons between different fluoride rinse features or fluoride rinses against other preventive strategies, and should evaluate adverse effects and acceptability.