Adolescents in the United States face crucial sexual health behavior issues, including consequences of sexually transmitted infections and diseases, pregnancy, and sexual violence. Lesbian, gay, bisexual, and transgender youth are disproportionately affected by these issues. State policies about sex education in K-12 schools shape what is taught to students about sexual health. In this study, we analyzed the content of school-based sex education policies of all 50 states and focuses on sexual behaviors, relationships, and identities. Policies analyzed include state statutes, state board of education policies, and state department of education or public instruction curriculum standards. Data were analyzed using content analysis. Most state policies emphasized abstinence from sexual behavior and did not require education about contraceptive and barrier methods. Few policies required detailed information about contraceptive and barrier methods to prevent pregnancy and sexually transmitted infections. Around half of states addressed relationship issues (ie, healthy relationships, sexual decision-making, and sexual violence); however, few states required content on communication about sexual consent. Eight state policies explicitly stigmatized homosexuality. Conversely, 12 states were inclusive of diverse sexual orientations and 7 states were inclusive of diverse gender identities. Sex education policies should be evidence-based and inclusive of sexual diversity.