Abstract
Sibling support for transgender and nonbinary (TNB) youth has the potential to improve TNB youths' mental health. A scoping review was conducted to map the knowledge of TNB youths' sibling relationships to create a foundation for the development of sibling-based support interventions for TNB youth. Nine included articles covered two areas: TNB youths' perceptions of sibling support (n = 5) and cisgender siblings' lived experience with a TNB sibling (n = 4). Siblings were perceived to support TNB youth, and their support was associated with less depression, suicidal ideation, and externalizing problems. Siblings of TNB youth lacked knowledge of TNB identities and support for their own understanding and acceptance. Siblings may experience unique stressors around their TNB sibling's changing gender identity. Overall, having a TNB sibling was perceived as a positive experience. None of the studies included intervention with or for siblings of TNB youth. Sibling support can be helpful for TNB youths' mental health. However, cisgender siblings' unique needs are rarely addressed. Providing cisgender siblings with knowledge of TNB identity, a place to process fears and concerns, and skills to navigate situations that may arise in relation to their sibling's gender, has the potential to benefit both siblings.