With the increasing life expectancy of adults with intellectual disability, though still shorter than peers in the general population, this group is now experiencing usual physical, cognitive and social aspects of ageing seen in the general population. In particular, this paper explores the question of whether or not having intellectual disability predisposes the individual to the development of dementia, a well-known age-related condition, in any inherent way. Although intellectual disability and dementia both impact upon cognition, the two conditions have vast differences in concept, etiology, neurobiology, diagnosis and approach to treatment. The paper reviews the epidemiological, genetic, neurobiological, and social evidence of possible associations between intellectual disability and enhanced risk of dementia development. In doing so it presents an approach to diagnostic, therapeutic, care, prevention, palliative, and medical aspects of dementia management in adults with intellectual disability who develop dementia, as well as practical aspects of working with disability sector professionals already involved in the care of adults with intellectual disability.