Background: Behavioural changes associated with dementia in Down syndrome are well documented, yet little is known about the effect of such behaviours on carers and referral. By comparing the behavioural and cognitive profiles of individuals referred for a dementia assessment with those of individuals not referred, some insight can be gained into behavioural characteristics that initiate referral for specialist support or interventions. Method: Forty-six adults with Down syndrome were divided into two groups dependent upon method of entry into the study; post-referral to a specialist service for older adults with intellectual disabilities and Down syndrome for a dementia assessment (n = 17) or after receiving information sent out to day centres and residential homes (n = 29). These groups were compared on established measures of dementia alongside two informant measures of behaviour. Results: Those referred for a dementia assessment evidenced scores indicative of cognitive decline on both informant and direct Neuropsychological Assessments and showed more behavioural excesses, but not deficits, and lower socialisation and coping skills than those in the comparison group. Carers of those referred for a dementia assessment reported a greater impact of behavioural excesses on staff than on the individual showing the behaviour in contrast to the comparison group. Conclusion: The behavioural differences between those referred and the comparison group suggest that two factors are involved in the instigation of a referral for a dementia assessment: the nature of the behavioural presentation (excesses rather than deficits) and the effect of that behavioural change upon the care staff.