It is well known that adolescents use the Internet for sexual purposes, for example viewing sexually explicit materials, a practice which increases with age. Prior research has suggested a link between cognitive and behavioral effects on the one hand and viewing sexually explicit materials on the Internet on the other. The present study aimed to explore exposure to sexually explicit materials on the Internet and a possible desensitizing effect on the perception of online sexual content over time. The study design was longitudinal; data were collected in 3 waves at 6 months intervals starting in 2012. The sample included 1134 respondents (girls, 58.8%; mean age, 13.84 ± 1.94 years) from 55 schools. A multivariate growth model was used for analyzing data. The results showed that the respondents changed their perception of sexually explicit material on the Internet over time depending on age, frequency of exposure and whether exposure was intentional. They became desensitized in terms of being less bothered by the sexual content. The results may indicate a normalization of sexually explicit material on the Internet during adolescence.