Sibling relationships play a crucial role in adolescent development, influencing emotional and psychological well-being through varying levels of warmth and hostility (for a review, see Buist et al., 2013; Fry et al., 2021). Given that siblings are some of the longest relationships an individual has across the lifespan (Kramer et al., 2019) and their contribution to socioemotional development during adolescence (Rogers & Morgan, 2024), facets of their relational dynamics are of key importance. The Texas Sibling Study (TSS) investigates these dynamics in 51 families using behavioral coding to assess warmth and hostility in sibling interactions using video recording observations of a conflict task. Understanding the impact of sibling hostility on adolescent mental health is essential for identifying factors that contribute to psychological well-being. I will examine how levels of hostility are associated with self-esteem, anxiety symptoms, and depression symptoms. I expect to see a significant positive association between sibling hostility and symptoms of anxiety and depression, such that higher levels of hostility will correspond with increased anxiety and depressive symptoms. Additionally, I expect a significant negative association between sibling hostility and self-esteem, indicating that greater hostility will be associated with lower self-esteem. The findings of this study may contribute to a deeper understanding of how sibling interactions can be associated with adolescent mental health, providing insight into how these dynamics influence holistic well-being.