OBJECTIVE To determine the frequency of asymmetries greater than 0.2 in the cup-to-disc ratio of a population of adolescents. METHODS Fundus photographs of both eyes of 123 adolescents were digitized at the resolution of 300 pixels per inch (300 dpi), 8 bits, with a RBG color pattern. The measurements were performed using the Image J software, version 1.42, developed by the National Institutes of Health (NIH), Java platform version 1.6. RESULTS The values of the differences in the cup-to-disc ratio between the two eyes of the same individual ranged from 0 to 0.30. The mean difference was 0.07, the median 0.06 and the standard deviation 0.05. About 54.4% of the studied population had asymmetries up to 0.06 and 79.7% had asymmetries up to 0.1. Two individuals presented asymmetries of more than 0.2, corresponding to 1.63% of the evaluated subjects. CONCLUSIONS The frequency of asymmetries in the group of adolescents studied was similar to that detected in studies of the normal adult population.