Sexual risk behaviors are sexual behaviors that are associated with an increased risk of a negative outcome such as the contraction or transmission of a disease or unintended pregnancy. This chapter presents an overview of these sexual risk behaviors and the prevalence of sexual risk behaviors among children and adolescents. Sexual behaviors including vaginal intercourse without a condom, anal intercourse without a condom, and oral sex without protection carry a high risk of contracting or transmitting an STI and becoming pregnant. The nature of the STI influences the risk for transmission of the STI to others lifespan. The chapter considers additional variables around youth's reports of being taught in school about AIDS or HIV infection. It identifies the sexual risk behaviors in which youth engage and the prevalence of the behaviours as measured by the Youth Risk Behavior Survey (YRBS).