Purpose Gender nonconformity (GNC) describes the degree of misalignment between individual's gender expression and gender norms and is often linked to negative health outcomes. We aimed to investigate the association between GNC and adolescent indoor tanning, the most preventable cause of skin cancer, among U.S. high school students. Methods This study examined cross-sectional data from the 2017 state Youth Risk Behavior Survey in Maryland. Participants included 25,432 female and 25,060 male students in grades 9 through 12. The primary outcome was the prevalence of self-reported 12-month history of indoor tanning before survey. The GNC was measured by self-perceived gender expression (from "very feminine" to "very masculine") and sex ("female" or "male"). The logistic regression analysis for weighted survey data was performed to estimate the association between GNC and adolescent indoor tanning. Results Among 50,492 high school students in Maryland, the prevalence of indoor tanning was 6.8(95% CI, 6.4-7.3), and varied by demographic characteristics and sexual orientation. Among male students, indoor tanning was significantly associated with moderate GNC (AOR, 1.55; 95% CI, 1.13-2.13; P=0.007) and high GNC (AOR, 4.92; 95% CI, 4.04-5.99; P<0.001). However, among female students, indoor tanning was not associated with moderate and high GNC in the adjusted models. Furthermore, indoor tanning was also significantly associated with transgender identity, the AOR was 7.16 (95% CI, 5.89-8.72; P<0.001) compared with cisgender female students, and 9.31(7.44-11.64; P<0.001) compared with cisgender male students. Conclusions Gender nonconforming adolescent males and transgender adolescents report higher risk of indoor tanning than gender conforming adolescent males and cisgender adolescents respectively. Skin cancer prevention efforts targeted at gender minorities might reduce indoor tanning, a preventable risk factor for skin cancer.