Sexual violence is a worldwide health and social issue. However, little is known about the sexual violence that occurs in the context of romantic relationships. This study analyzes the existence of sexual violence in adolescents’ romantic relationships, the possible associations between such violence (both committed and suffered) and myths about sexual aggression and sexual assertiveness, and the possible gender-related distinctions. A sample of 329 students aged between 15 and 19 (M = 16.3; SD = 0.79) was surveyed; all participants were in a romantic relationship when the data were collected. The results reveal that both genders report the existence of sexual violence in their romantic relationships; however, in heterosexual relationships, males were more often the perpetrators of sexual violence. Additionally, myths about sexual aggression and sexual assertiveness were found to be significantly associated with both perpetration and victimization. Accordingly, these predictors should be focal points in prevention programs for adolescent sexual violence. The findings of this study show the de-prioritization of sexuality education in the Spanish educational system, as well as the need to strengthen the competence of adolescents in this area.