OBJECTIVE To demonstrate that the application of dental fluoride varnishes in children increases urinary fluoride excretion. METHODS From a randomly assembled group of 42 children aged between 5 and 8 years, residing in a community with non-fluoridated water, spot urinary samples were taken before the topical application of dental fluoride varnish and 2 hours afterwards. In an age-matched control group of 16 children from the same community, who received no treatment, samples were taken the same way. The urinary excretion of fluoride was analysed by determining fluoride ion (F-) level and fluoride/creatinine (F/Cr) ratio in the urine. RESULTS In the study group, the average pre- and post-treatment F/Cr ratios were 0.42 and 1.38 mg/g, respectively (p < .001). No significant changes were observed in the control group, which received no treatment. The average 2 hours afterward F/Cr ratios were 0.29 and 0.27 respectively (p = 0.426). CONCLUSIONS The topical application of dental fluoride varnish leads to a significant increase in urine F-, which is attributable to the application of the product.