Abstract <p>Developing best practices for accurately ascertaining gender identities has become increasingly important, especially as more adolescents identify with transgender and nonbinary identities. The research community faces the challenge of creating inclusive and representative measures that effectively capture these identities. In collaboration with the Adolescent Medicine Trials Network for HIV Interventions (ATN), we present our youth-informed multi-step process for gender, gender identity and sex-assigned-at-birth ascertainment. We also highlight the critical need to involve adolescents directly in the development and testing of affirming and intersectional gender identity measures, with particular attention to ensuring how language reflects race, ethnicity, and tribal affiliation among other backgrounds. By engaging adolescents in the creation and refinement of these measures, researchers can develop methodologies that not only enhance data quality and accuracy but ensure the correct recognition of unique identities.</p> Impact <p>This article shares a newly developed, affirming, multistep process to measure gender in adolescent research while highlighting the importance of their involvement in the developmental process.</p>