Dental fluorosis and caries incidence in children: a longitudinal study. To assess whether the incidence of dental caries differed in groups of individuals with different levels of dental fluorosis. At baseline, 1662 participants of a population-based cohort study underwent a dental fluorosis evaluation using Dean's index and the severity of dental fluorosis was recorded using the Thylstrup-Fejerskov Index (TFI). The outcome was first occurrence of at least one dentinal lesion on one or more surfaces of one or more posterior teeth at follow-up. After 10 years of follow-up, the first carious lesion was found in 12.3% (n = 193) of the participants. The first carious lesion was found in 26.8% of the children with no fluorosis, in 14.9% with mild fluorosis, in 11.9% with moderate fluorosis, and in 3.3% with severe fluorosis (P < 0.001). The first carious lesion developed more frequently in individuals with fluorosis grades 1 and 2 (TFI < or = 1) compared with individuals with fluorosis grade 0 (TFI = 0) (odds ratio: 1.69; 95% confidence interval (CI): 1.22-2.33). In the multivariate analysis, severe fluorosis grade (TFI = 4), absence of posterior tooth contact, and a higher level of plaque (P < 0.001) were protective factors against dental caries. Results show an inverse association between dental fluorosis and dental caries, with a greater reduction in the odds of being affected in severe grades of fluorosis. Toothbrushing instruction should focus on individuals with fluorosis grade 1 and 2 and the frequency should be more intensive and focused on reducing plaque accumulation in these individuals.