Objectives: To evaluate the efficacy of weekly supervised tooth-brushing with a toothpaste and a 1.23% acidulated phosphate fluoride gel (APF) gel on white lesion reversal to treat incipient enamel lesions. Design: A double-blind and randomized controlled trial. Sample and Methods: Three-hundred seven to 12-year-old Brazilian schoolchildren who presented with white spots on the buccal surfaces of permanent upper incisors were randomly allocated to three groups. In group I, children underwent supervised tooth-brushing and APF gel (1.23%) for one minute once a week. In group II, children were subjected to a weekly supervised tooth-brushing and a topical application of placebo, whereas group III (control) received no intervention. An expert dental examiner performed all intra-oral examinations for dental caries (DMF-s and dmf-s) and oral hygiene (Visible Plaque Index, Gingival Blood Index). Results: After three months, 258 children and 460 lesions were analyzed. The results of the clinical evaluation of arrested white spots did not differ significantly (p = 0.95) between the two experimental groups (57.9% in group I and 56.8% in group II) but differed significantly between them and the control group (p = 0.022). Logistic regression analysis identified gingival blood index (OR = 1.70, CI = 1.13 - 2.55), DMF - s2 (OR = 1.61, CI = 1.07 - 2.43) and number of white spot lesions (OR = 1.76, CI = 1.04 to 2.98) as independent 'risk' factors for white spot lesion activities. On the other hand, supervised tooth-brushing with APF (OR = 0.55, CI = 0.34 - 0.91) or without APF (OR = 0.58, CI = 0.35 - 0.94) was a protective factor. Conclusions: These results suggest that the weekly supervised tooth-brushing was able to arrest enamel white spots and that poor oral hygiene increases the probability of keeping white spots active. Keywords: acidulated phosphate fluoride, dental caries, enamel demineralization, randomized controlled trial