Siblings are important in the lives of individuals with an intellectual disability and pervasive support needs; however, adults' experiences of the things they do with or for their siblings with pervasive support needs remain underexplored. This study examined positive and challenging aspects of their roles related to their siblings. An online questionnaire was completed by 55 adults whose siblings had pervasive support needs. An inductive approach was used to thematically analyze open-ended questions about their experiences. The respondents described rewarding experiences of being with their siblings, combined with a sense of care and responsibility, and noted how their experiences were affected by their siblings' support needs. "Being of service" was experienced as both rewarding and as a demanding responsibility. Collaboration with family members and health care professionals was another overarching theme. Our findings highlighted the valuable mutual contributions of siblings in each other's life when one of them has pervasive support needs. Understanding adults' experiences relating to their siblings who have pervasive support needs enables service providers to facilitate their contact and support. In addition, these findings can provide input for government agencies and organizations that provide support for people with disabilities by increasing awareness about siblings' perspectives.