Siblings often oversee the well-being of an adult with autism spectrum disorder (ASD). The current study contributes to the literature by examining correlates of support provided to siblings in young adulthood in the context of the broader autism phenotype (BAP). Young adults (n = 866; M[subscript age] = 25.43, SD = 2.54; 55% female) reported on support provided to and the BAP characteristics of 1198 different siblings (M[subscript age] = 28.56, SD = 8.87; 50% female). Findings showed that young adults provided more emotional and practical support to sisters that they perceived to be higher in BAP characteristics. These findings suggest that sisters who have characteristics associated with ASD may be at an advantage in receiving support.