Background: Young people may experience school-based violence and bullying victimization related to their gender expression, independent of sexual orientation identity. However, the associations between gender expression and bullying and violence have not been examined in racially and ethnically diverse population-based samples of high school students. Methods: This study includes 5469 students (13-18 years) from the 2013 Youth Risk Behavior Surveys conducted in 4 urban school districts. Respondents were 51% Hispanic/Latino, 21% black/African American, 14% white. Generalized additive models were used to examine the functional form of relationships between self-reported gender expression (range: 1 = Most gender conforming, 7 = Most gender nonconforming) and 5 indicators of violence and bullying victimization. We estimated predicted probabilities across gender expression by sex, adjusting for sexual orientation identity and potential confounders. Results: Statistically significant quadratic associations indicated that girls and boys at the most gender conforming and nonconforming ends of the scale had elevated probabilities of fighting and fighting-related injury, compared to those in the middle of the scale (p < 0.05). There was a significant linear relationship between gender expression and bullying victimization; every unit increase in gender nonconformity was associated with 15% greater odds of experiencing bullying (p < 0.0001). Conclusions: School-based victimization is associated with conformity and nonconformity to gender norms. School violence prevention programs should include gender diversity education.