Objectives: To assess the impact of differing degrees of enamel fluorosis on dental aesthetics according to Irish adolescents. The same participants also aesthetically rated other variations in dental appearances including a carious lesion, bleached teeth and a demarcated opacity. Methods: One hundred and fifty adolescents examined seven identical template photographs of an attractive dental smile displaying varying levels of enamel fluorosis (TF1, TF2, TF3), a demarcated opacity, no fluorosis (TF0), anterior caries and very white or bleached teeth. By indicating their level of agreement or disagreement with five statements on a five-point Likert scale, the participants rated the aesthetic acceptability of each of the photographs. Results: Using paired t-tests with the Bonferroni correction, it was found that the photographs depicting the very white teeth and anterior caries were rated as the most and least aesthetically pleasing images, respectively. There was no significant difference in the ratings of the photographs displaying TF0, TF1 and TF2 levels of fluorosis indicating that these photographs were viewed similarly (P > 0.002). The remaining two photographs (TF3 and the demarcated opacity) were rated similarly and significantly worse (P < 0.002) than the photographs showing no or low grades of fluorosis (TF0, TF1 and TF2). Conclusions: TF3 level of fluorosis represented the break point at which enamel fluorosis became aesthetically objectionable to these participants. Low grades of fluorosis (TF1 and TF2) were rated similarly to the photograph depicting no fluorosis (TF0).