METHODS Cochrane Oral Health Group Trials Register, Cochrane Central Register of Controlled Trials (CENTRAL), Medline, Embase and CINAHL. METHODS Randomised controlled trials (RCTs) comparing the effects of chlorhexidine-containing oral products with no treatment or placebo on dental caries, and comparing the effects of one chlorhexidine-containing oral product with another were considered. METHODS Two reviewers independently extracted trial data and assessed risk of bias. Owing to the clinical diversity of the included studies with respect to age, composition of intervention, and variation in outcome measures and follow-up, meta-analysis was not carried out. A narrative synthesis was presented. RESULTS Eight trials were included. Six were at high risk of bias and two at unclear risk. Six trials compared chlorhexidine varnish with placebo or no treatment. Data from two trials (690 patients) one using 10% chlorhexidine varnish and the other, 40%, showed that this led to an increase in the DMFS increment in the varnish group of 0.53 (95% CI; -0.47 to 1.53). Only one trial involving 496 patients and using 10% chlorhexidine varnish provided usable data for elevated mutans streptococci levels > 4 with RR 0.93 (95% CI; 0.80 to 1.07). Two trials (487 patients) compared 0.12% chlorhexidine gel with no treatment in the primary dentition. The presence of new caries gave rise to a 95% confidence interval that was compatible with either an increase or a decrease in caries incidence (RR 1.00, 95% CI 0.36 to 2.77). CONCLUSIONS The authors found little evidence from the eight trials on varnishes and gels included in this review to either support or refute the assertion that chlorhexidine is more effective than placebo or no treatment in the prevention of caries or the reduction of mutans streptococci levels in children and adolescents. There were no trials on other products containing chlorhexidine such as sprays, toothpastes, chewing gums or mouthrinses. Further high quality research is required, in particular evaluating the effects on both the primary and permanent dentition and using other chlorhexidine-containing oral products.