Background: Previous studies found that a school climate of more heteronormativity is associated with adverse effects on the mental health of LGB students. Accordingly, our aim was to assess the association between low LGB visibility in schools and unhealthy weight-control behaviors among LGB youth. Methods: Cross-sectional, multilevel study based in public high schools in the city of Olinda, Northeast Brazil. A multilevel logistic regression was performed, including 2,500 adolescents enrolled in 27 schools. The contextual variable was the prevalence of LGB youth in each school (as a proxy for heteronormativity in schools) while the outcome was unhealthy weight-control behaviors (fasting, purging, and taking diet pills). We controlled for socioeconomic characteristics (age, gender, receiving a family allowance), obesity, and self-reported happiness. Results: Low LGB visibility in schools was associated with higher odds of engaging in unhealthy weight-control behaviors (OR: 1.5, 95%CI: 1.0, 2.2) among all youth, regardless of sexual orientation. Among LGB youth, there was some suggestion that the association between LGB visibility and unhealthy weight control behaviors was mediated by experiences of victimization and self-perceptions of unhappiness.Conclusion: A school environment of low LGB visibility was associated with unhealthy weight-control behaviors in youth.