Dental fluorosis is a developmental defect of enamel caused by chronicand excessive fluoride intake resulting in a hypomineralized enamel withincreased porosity. It is clinically identified as spots ranging from mild whitelines to opaque spots covering all or part of the enamel surface andbreakdown after teeth eruption. However, the clinical definition of the fluorosisdegree in teeth is not an easy task, having been presented many indicesthat generally qualify the severity degree with variations in the details.As the choice of treatment is closely linked to the defect severity, the purposeof this article is to present the clinical aspects of dental fluorosis representedthrough the Thylstrup-Fejerskov Index. The severity scores arepresented according to histological features and the differences betweenthem will be discussed in order to enable the dentist to correctly diagnoseand choose the most appropriate treatment for the patient with DF.