This research aimed to determine the influence of fluoridated groundwater and 1,100 ppm fluoride dentifrice on biomarkers of exposure to fluoride in preschoolers. A cross-sectional study was performed on thirty preschoolers recruited from naturally fluoridated and non-fluoridated areas (n=15). Total Daily Fluoride Intake (TDFI) from diet and dentifrice, and Daily Urinary Fluoride Excretion (DUFE) was measured over 24 h. Nails samples were collected twice during 30 days. Fluoride analyses were performed using a fluoride-ion-specific electrode. Data were evaluated using the Student and paired t-test, Pearson correlation analysis, multiple linear regression analysis (α≤0.05). Fluoridated groundwater and dentifrice were the dominant sources (r2 > 0.83) of TDFI in children from a naturally fluoridated and a non-fluoridated area, respectively. A positive correlation between TDFI and DUFE (r=0.50), and between [F] in fingernails and toenails (r=0.60) were found in children from a naturally fluoridated area. The [F] in nails of finger and toe were not correlated to TDFI. The consumption of fluoridated groundwater influenced the fluoride concentration in urine. In addition, the use of 1,100 ppm fluoride dentifrice did not influence the fluoride concentration in urine and fingernails.