Cancer incidence and prevalence in people with intellectual disabilities are poorly documented. Changing demographic patterns, however, mirror those in the general population with increased longevity leading to higher numbers of people developing cancer in the future. Little is known about the service and support needs of this group, but there is a precedent to understand their experiences to inform research and service development if appropriately tailored approaches are to be adopted. This article outlines a project that sought to develop an advisory forum of adults with intellectual disabilities affected by cancer, to inform the development of a research agenda. The process of this work is described alongside a critical appraisal of the tensions in involving people with intellectual disabilities as advisors on cancer research and practice. We discuss and challenge the underlying ideologies, which lie in the path of fully engaging with marginalized patients.