Purpose: To clinically evaluate the effectiveness of resin infiltration in conjunction with fluoride varnish treatment vs fluoride varnish treatment alone on facial smooth-surface caries lesions in deciduous teeth. Materials and Methods: This randomised clinical trial was conducted in 419 children aged 18-71 months with at least two active smooth-surface caries lesions in deciduous teeth (ICDAS II score 2). Eighty-one participants met the inclusion criteria and were allocated to one of the two treatment groups: resin infiltration and fluoride varnish (RI+FV) (n = 41) and fluoride varnish only (FV) (n = 40). The prevalence of treated white spot lesions (WSL) was scored. Fluoride varnish was applied in both groups every 3 months for a year. Results: The mean baseline age of children was 3.8 ± 1.3 years. The effectiveness of resin infiltration measured as the percentage of children who did not present any progression of the treated lesions amounted to 43.1%. After one year, 92.1% of the infiltrated lesions (RI+FV) and 70.6% of the FV lesions had not progressed (p 0.001). Conclusion: Resin infiltration in conjunction with fluoride varnish treatment of early facial smooth-surface caries lesions in deciduous teeth is superior to fluoride varnish treatment alone for reducing lesion progression. Palabras clave: early caries lesions, fluoride varnish, randomised clinical trial, resin infiltration