AIM: This study has evaluated the knowledge about dental fluorosis and the behavior of young people regarding to the use of Fluor. MATERIAL AND METHODS: 313 students from High School of Tabatinga/SP, from 15 to 21 years old have answered a questionnaire with pre-encoded questions in which was approached the variables: gender, age, schooling level, dwelling, water consumption, oral hygiene habits, frequency of consults to the dentist and perception about clinical characteristics of fluorosis. Data obtained were analyzed by means of descriptive statistics. RESULTS: There was female prevalence (56.0%). Most of respondents (81.0%) answered brushing the teeth 3 times or more a day. About dentifrice use and quantity on the toothbrush, from 97% who has asserted using them, 58% cover all the bristles; 88% of participants know Fluor; however, regarding to its function or effect on the teeth, 17% and 32%, respectively, have not known how to answer. About water consumption, most of them consume from 1 to 2 liters a day, and the main source is the “faucet” (47%). It was observed that 49% of interviewees have visited the surgeon dentist less than one month ago; 93% have answered that the topic application of Fluor was carried out during the dentist consultation, and 32% have asserted that the application was performed in all the visits. Regarding the surface stains on tooth enamel, 59% have reported that they did not notice them; however, 21% have noticed white stains on the enamel. Regarding to the use of tooth paste in the childhood, 52% have reported that they used to ingest it. CONCLUSION: Young’s knowledge about function and effect of Fluor on dental structures were mistaken, once the concept of dental cleaning was prevalent about prevention of caries, and the behavior about fluoridated toothpaste was inappropriate because they use it excessively, and they also asserted its ingestion in the childhood.