This article evaluated the prevalence and factors associated with risky sexual behavior (RSB) among Brazilian school adolescents. This is a cross-sectional study with data collected from the National Survey of School Health, 2019 edition, with a representative sample of 7th grade of elementary school to 3rd year of high school Brazilian school adolescents. This work evaluated sociodemographic, behavioral, sexual and reproductive health, mental health, sociability characteristics, medical advice received at school, and body image. RSB was characterized as the non-use of a condom during sexual intercourse. The data were analyzed using hierarchical Poisson regression modeling. The prevalence of RSB was of 40.3%, with the lowest proportion appearing in the North region (37.4%). The highest prevalence of RSB was found among female adolescents, whose first sexual intercourse occurred at 13 years of age or under, who were victims of sexual violence, who practiced bullying, and who used illicit drugs, cigarettes, and alcohol. Those who used a condom during their first sexual intercourse showed the lowest prevalence of RSB. The high prevalence of RSB among Brazilian school adolescents, together with the knowledge of the associated factors, serves to define strategies to favor improvements in the sexual and reproductive health of these young people.