The diagnosis of dementia in Alzheimer's disease remains at times problematic in adults with intellectual disability. The analysis of 5-year consecutive data developed a researched-based clinical screening tool for dementia in Alzheimer's disease in adults with Down syndrome. The Adaptive Behaviour Dementia Questionnaire (ABDQ) is a 15-item questionnaire, which is used to detect change in adaptive behaviour. The scale has good reliability and validity, with an overall accuracy of 92%. It is the first clinical tool designed specifically to screen for dementia in Alzheimer's disease in adults with Down syndrome.