Parents often provide the bulk of caregiving supports for their adult offspring with intellectual and developmental disabilities (IDD). Given the longer lives of people with IDD, however, such caregiving roles may transition to siblings. Thus, it is critical to conduct future planning among family members (e.g., parents, siblings) to prepare for the transition of caregiving roles. To this end, we interviewed 10 parent-sibling dyads (N = 20) of people with IDD about long-term planning. Both parents and siblings reported family-related and systemic barriers to developing future plans. Siblings (unlike parents) reported wanting more communication among family members about planning. Implications for future research and practice are discussed.