Research has shown that lesbian and gay (LG) individuals are coming out not only to their parents, but also to their siblings. Eighty percent of individuals in the United States are raised with one or more siblings; however, researchers have frequently underestimated the importance of the sibling bond. This study examined potential correlates of heterosexual siblings' acceptance of their LG sister or brother using an online survey format (N = 189). In addition, psychometric properties for the Acceptance of Sibling Sexual Orientation Scale are provided. Results revealed that greater sibling relationship quality in adulthood, more contact with LG individuals, greater knowledge of LG communities, more support for LG civil rights, and various demographics (being female, having higher educational levels, not having an orthodox/fundamentalist religious orientation, less church attendance, and more liberal political ideology) are related to heterosexual siblings' acceptance of their LG sister or brother. However, when these variables were examined together in a regression model, only sibling relationship in adulthood, contact with LG individuals, support for LG civil rights, and religious attendance were significant unique predictors of acceptance.