Background: It is becoming more common for siblings to fulfill a caregiving role for their brother or sister, particularly because people with intellectual/developmental disabilities (IDD) are often living longer and outliving their parents. However, most of what we know about siblings of people with IDD is based on research with children, and limited studies on the adult sibling experiences in Canada have been published. To meet the support needs of Canadian adult siblings, "The Sibling Collaborative", a grass‐roots initiative, conducted a needs assessment. Specific Aims The purpose of this study was to better understand the current challenges siblings experience and how requested resources may differ across three age groups: adults between the ages of 20 and 29 years, 30 to 49 years, and 50 years of age and older. Method A total of 260 siblings of individuals with IDD from across Ontario completed an online survey. Findings Siblings endorsed a relatively low rating of intensity of support that they provided for their brothers or sisters with IDD at the time of survey completion; however, the majority indicated that they intended to take a greater caregiving role in the future. Ratings of support differed by sibling age groups, as did challenges related to supporting brothers or sisters with IDD. Overall, participants reported a range of desired resources and preferred methods of accessing resources. Discussion Siblings' caregiving relationships with their brothers and sisters with IDD differed across age groups. Results from the current study indicate different supports may be needed for different age groups. As policies around the world continue to encourage continued family involvement in caregiving for adults with IDD, it is important to understand how systems can better support sibling caregivers.