ABSTRACT Rough sexual behaviors (i.e., sex that involves slapping, hard spanking, punching, choking, and/or other physically aggressive acts) appear to be increasingly common among adolescents and young adults (ages 15– 29; AYA) in the United States (US). Rough sex can have negative mental and sexual health consequences for AYA. Even when rough sex is consensual, it can cause injury (e.g., concussion, bruising, lacerations) and—in rare cases—death. Further, preliminary data suggests that youth may feel pressured or coerced into rough sex. In these cases, the distinction between rough sex and sexual assault is unclear and the after-effects may mirror those experienced by sexual assault survivors including an increased likelihood of physical and emotional dating abuse; depression, anxiety, and trauma symptoms; unintended pregnancy; and sexually transmitted infection (STI). Lastly, some AYA may consent to rough sex, only to be unprepared for the level of intensity or aggression used by their partner or the health consequences of those actions. This differentiation between expectations and experience may prove to be emotionally harmful in addition to any physical harm that is caused. Presently, there are no national estimates of the prevalence of rough sexual behaviors across adolescence and young adulthood. There is an urgent need for us to assess the prevalence and diversity of rough sexual behaviors among AYA, explore which factors influence whether and how AYA engage in rough sex (e.g., partners, peers, media), and examine how engaging in rough sex relates to the mental and sexual health of AYA. As such, the aims of this sequential explanatory mixed-methods study are to: (1) use a nationally representative survey of 800 adolescents (15–17 years old) and 1,000 young adults (18–29 years old) to determine the prevalence and correlates of rough sexual behaviors among AYA in the US; (2) conduct follow-up in-depth interviews with a diverse subsample of AYA from Aim 1 (N = 150) to assess how rough sex behaviors are understood, experienced, and related to health by AYA; and (3) examine whether rough sex experiences, expectations, and consequences vary for demographic subgroups. A youth advisory board will be involved in all stages of the study. This study will provide critical information about the prevalence, correlates, and consequences of rough sex, including how rough sex relates to the mental and sexual health of AYA. Results will inform meaningful and impactful mental and sexual health programming aimed at addressing sexual assault, mental health, unintended pregnancy, and STI acquisition among AYA.