Purpose: To clinically evaluate the additional effect of adding 0.12% chlorhexidine digluconate (CHX) to a 0.05% sodium fluoride (NaF) mouth rinse in arresting active enamel caries lesions after 28 days. Materials and Methods: A short-term double-blind clinical trial that included a total of 170 children, aged 11 to 15 years, with active smooth surface caries lesions (average 6.52) was conducted. The participants were enrolled and randomly distributed into two equal groups. Under the supervision of the research team, the children rinsed with a 15 ml solution of either 0.05% NaF (G1) or 0.05% NaF + 0.12% CHX (G2) for 1 min/day for 28 days. A clinical examination was carried out at the beginning and at the end of the study with children who underwent supervised tooth brushing. A calibrated examiner, who was unaware of the treatment given to each subject, examined all smooth surfaces dried with compressed air, isolated and illuminated with a reflector. The surface was considered active (A) or arrested (I). The frequency of A or I surfaces was evaluated by calculating the difference between the number found at the beginning and at the end of the trial. Results: No significant differences were detected between the two groups with respect to caries lesion surfaces at baseline (6.49 ± 4.45 - G1, 6.55 ± 4.23 - G2, respectively), nor were differences found when age and gender were taken into consideration. Arrestment proportions were 84.4% (G1) and 85.3% (G2) (P = 0.71; not significant). Conclusions: Although both solutions showed high arrestment proportions, the addition of CHX did not improve the arrestment capacity of the NaF mouth rinse. Keywords: chlorhexidine, dental caries, fluoride, randomised controlled trial