Siblings of brothers or sisters with intellectual and developmental disabilities (IDD) are important but understudied family members. As many previous studies have relied on parent report of sibling outcomes, the use of sibling self-report is an important addition to the research. This study assessed the feelings of adolescent siblings toward their brothers or sisters with and without IDD, as well as broader aspects of sibling empathy. Data were collected via a national, online survey from 97 parent-sibling pairs. Siblings of individuals with IDD reported higher levels of anxiety toward the target child than did siblings of typically developing individuals. Sibling feelings toward the target child were related to both parental and target child factors, but only among families of individuals with IDD.