The present study investigated the relationship between different types of sexual media use (i.e., sexually explicit internet material, sexually oriented reality TV, and sexy self‐presentations on social network sites) and adolescents' willingness to engage in casual sex, as well as underlying sociocognitive processes of this relationship. Drawing on a longitudinal three‐wave panel study among 1,467 adolescents (aged 13–17, 50% female), we found that exposure to sexually explicit Internet material directly predicted adolescents' willingness to engage in casual sex. Exposure to sexy self‐presentations of others on social network sites and sexually oriented reality TV predicted adolescents' willingness to engage in casual sex indirectly through descriptive peer norms on casual sex.