The aim of this study was to assess in vivo the therapeutic effect of three fluoride varnishes available in the Brazilian market on the performance of white spot lesions (WSL). The sample included 36 children aged 7 to 13 years old, with a total of 67 active WSL in permanent anterior teeth. The children were randomly divided into 3 groups, according to fluoride varnish used: FL-Fluorniz (n=24), DUO -Duofluorid XII (n=22) and DF -Durafluor (n=21). Maximum WSL dimensions (mesiodistal and incisogingival) were measured in millimeters by a previously calibrated single examiner using a periodontal probe. WSL were also assessed regarding lesion activity. Initial and final S-OHI (Simplified Oral Hygiene Index) scores were recorded. Pearson's chi-square test revealed no statistically significant differences (p>0.05) in the performance of the varnishes. At the end of the 5th week, FL had 6 active and 18 inactive WSL; DUO had 7 active and 15 inactive WSL; and DL had 6 active and 15 inactive WSL. Taking into account all lesions, there was a 45.7% reduction in WSL dimensions. Paired Student's t-test revealed a statistically significant difference (p<0.05) between the initial size (1.88) and final size (1.02). After four applications, all varnishes obtained similar clinical results.