IMPORTANCE Sexual violence can emerge in adolescence, yet little is known about youth perpetrators-especially those not involved with the criminal justice system. OBJECTIVE To report national estimates of adolescent sexual violence perpetration and details of the perpetrator experience. DESIGN, SETTING, AND PARTICIPANTS Data were collected online in 2010 (wave 4) and 2011 (wave 5) in the national Growing Up With Media study. Participants included 1058 youths aged 14 to 21 years who at baseline read English, lived in the household at least 50% of the time, and had used the Internet in the last 6 months. Recruitment was balanced on youths' biological sex and age. MAIN OUTCOMES AND MEASURES Forced sexual contact, coercive sex, attempted rape, and completed rape. RESULTS Nearly 1 in 10 youths (9%) reported some type of sexual violence perpetration in their lifetime; 4% (10 females and 39 males) reported attempted or completed rape. Sixteen years old was the mode age of first sexual perpetration (n = 18 [40%]). Perpetrators reported greater exposure to violent X-rated content. Almost all perpetrators (98%) who reported age at first perpetration to be 15 years or younger were male, with similar but attenuated results among those who began at ages 16 or 17 years (90%). It is not until ages 18 or 19 years that males (52%) and females (48%) are relatively equally represented as perpetrators. Perhaps related to age at first perpetration, females were more likely to perpetrate against older victims, and males were more likely to perpetrate against younger victims. Youths who started perpetrating earlier were more likely than older youths to get in trouble with caregivers; youths starting older were more likely to indicate that no one found out about the perpetration. CONCLUSIONS AND RELEVANCE Sexual violence perpetration appears to emerge earlier for males than females, perhaps suggesting different developmental trajectories. Links between perpetration and violent sexual media are apparent, suggesting a need to monitor adolescents' consumption of this material. Victim blaming appears to be common, whereas experiencing consequences does not. There is therefore urgent need for school programs that encourage bystander intervention as well as implementation of policies that could enhance the likelihood that perpetrators are identified.