Media may function as sex educators for adolescents; unfortunately, media messages often glamorize risky sexual behaviors and unhealthy relationships and neglect sexual health behaviors and communication. Media Aware is a web-based comprehensive sexual health program for high school students that uses a media literacy education approach. It is designed to improve adolescents’ critical thinking about media messages and provide medically-accurate information and skills building related to sexual health and communication. A randomized controlled trial was conducted in 2019-2020 with students (grades 9 and 10; n = 590) from 17 high schools across the United States. The sample was 53% female, 58% white/Caucasian; and 13% Hispanic/Latinx. One high school teacher per school and all of their 9th and 10th grade students were randomly assigned to either the intervention or delayed-intervention (control) condition. The study assessed the immediate (posttest) and short-term (3-month) effects of Media Aware on adolescents’ media, sexual health, and communication outcomes. For 9 of the 17 schools, students were home from school due to the beginning of the COVID-19 pandemic during the time of their 3-month data collection, which left the short-term analyses underpowered. However, several impacts of the program were found in the immediate posttest analyses. Media Aware was found to improve sexual health knowledge and redress inaccurate normative beliefs about the frequency of risky teen sex. Media Aware also improved critical thinking about media messages with demonstrated improvements in media message deconstruction skills and decreases in the perceived realism of media messages. Moderator analyses found some differential immediate effects of the program attributable to gender. Media Aware reduced girls’ normative beliefs about teen sex, generally, and increased their sexual health communication with parents as well as reduced boys’ acceptance of dating violence. Students gave positive feedback about Media Aware, especially related to the online format of the program. The results from this study provide evidence that Media Aware is an effective web-based program for positively enhancing high school students’ media, sexual health, and sexual health communication outcomes.