<p></p><p>Abstract Introduction External control is the monitoring of fluoride concentration in the water supply that must be done by state institutions, and has been motivated to ensure the efficacy and safety of fluoridation. This study aimed to analyze the external control of municipalities with more than 50.000 inhabitants in the metropolitan region of Curitiba in the years 2014 and 2015. Methodology Health surveillance services of the studied municipalities provided external control data, which were analyzed according to the technical criterion of the CECOL for fluoride content. Results Collection of water samples failed in some municipalities and months for an adequate number for the fluoride parameter. From the total samples analyzed, only 51.5% were in the best benefit-risk range for the fluoride concentration. Eight percent of the samples presented insignificant benefit and risk and 0.1% showed a high-risk fluoride concentration, without any benefit. Conclusion the analyzed municipalities performed the external control, with periods of inadequate sample collections. Fluoride concentrations in the supply water of the study municipalities presented an unsatisfactory result. The main goal of external control is to maintain fluoride levels at adequate levels.</p><p></p
