Some researchers and clinicians may feel hesitant to assess sexual orientation and gender-related characteristics in youth surveys because they are unsure if youth will respond to these questions or are concerned the questions will cause discomfort or offense. This can result in missed opportunities to identify LGBTQ+ youth and address health inequities among this population. The aim of this study was to examine the prevalence and sociodemographic patterns of missingness among survey questions assessing current sexual orientation, gender identity and expression (SOGIE), and past change in sexual orientation (sexual fluidity) among a diverse sample of U.S. youth. Participants ( = 4,245, ages 14-25 years; 95% cisgender, 70% straight/heterosexual, 53% youth of color), recruited from an online survey panel, completed the Wave 1 survey of the longitudinal Sexual Orientation Fluidity in Youth (SO*FLY) Study in 2021. Current SOGIE, past sexual fluidity, and sociodemographic characteristics were assessed for missingness. Overall, 95.7% of participants had no missing questions, 3.8% were missing one question, and 0.5% were missing ≥ 2 questions. Past sexual fluidity and assigned sex were most commonly missing. Sociodemographic differences between participants who skipped the SOGIE questions and the rest of the sample were minimal. Missingness for the examined items was low and similar across sociodemographic characteristics, suggesting that almost all youth are willing to respond to survey questions about SOGIE. SOGIE and sexual fluidity items should be included in surveys and clinical assessments of youth to inform clinical care, policy-making, interventions, and resource development to improve the health of all youth. (PsycInfo Database Record (c) 2024 APA, all rights reserved).