The objective of this work is to measure the fluoride ions in the groundwater in the region of Khouribga, The Great Basin phosphated in Morocco constitutes the basin of Ouled Abdoun and known of its effect on the groundwater table of Tadla which feeds the whole region. All the samples have been extracted in an area where there is an activity of the Phosphate Plant, which extends from the city of Khouribga up to the city of Oued-Zem. Ninety samples have been collected from the different douars that exist in this area. These samples have been selected because of the activity of the OCP, and also as a function of the population that has been affected and show signs of fluorosis; the dental disease caused mainly by the excess of fluoride ion in the waters of drink. After the transport of samples to the laboratory of Hydrology within the National Institute of Hygiene of Rabat, the measurement of fluoride ions has been made by the specific electrical to ions F-. The values found vary from 0.08 mg/L to 1.93 mg/L, and their standard deviation is 0.54 mg/L ± 0.45 mg/L, which indicates that some samples are loaded with fluorine. Thus, we conclude the emergence of fluorosis among the population that uses the groundwater as a drinking water.