Background <p>Suicide rates among U.S. preteens (ages 8–12) have risen steadily since 2008, signaling a growing crisis in children’s mental health. Sexual and gender diverse (SGD) preteens are at especially high risk, with recent findings showing 4–6 times higher risk of suicidal thoughts and behaviors among sexual minority preteens and up to 14-fold higher risk among transgender preteens. Despite these alarming disparities, SGD preteens are often excluded from suicide research due to ethical, legal, and methodological barriers. There is a pressing need for expert-informed best practices to safely and ethically include this population in research.</p> Methods <p>We conducted a three-step Delphi process to develop expert-informed guidelines for ethically and effectively engaging SGD preteens at elevated risk in suicide research. The process was shaped by input from youth and adult community advisory boards and included 20 expert panelists across five overlapping roles: researchers, clinicians, legal/regulatory professionals, bioethicists, and community leaders. Experts completed a first-round survey, a structured virtual consensus meeting, and a second-round survey.</p> Results <p>Consensus was reached across multiple domains including developmentally appropriate criteria for SGD identity classification in research as well as criteria for classifying heightened suicide risk in preteens. Experts agreed that SGD identity alone should not be used as a proxy for risk nor should any preteens be excluded from research based on clinical severity of symptoms. Experts highlighted feasible sampling methods including convenience and purposive sampling and recruitment and retention strategies aimed at both youth and caregivers. Experts agreed on study safeguards such as provision of mental health resource lists and parental notification if structured risk thresholds were exceeded during research. There was full agreement on the importance of IRB review by individuals with child mental health and SGD expertise, although experts did not achieve consensus on the feasibility of implementing any IRB reforms.</p> Conclusions <p>This multi-phase Delphi study produced expert-endorsed recommendations for safely, ethnically, and effectively including SGD preteens at elevated suicide risk in research. These guidelines provide a foundation for inclusive, community-engaged suicide research with vulnerable youth.</p> Clinical trial number <p>Not applicable.</p>