Background: Different interview schedules and diagnostic criteria for dementia have contributed to differing incidence and prevalence rates.

Aim: This study aimed to examine the effect of different diagnostic criteria on the prevalence of dementia in the community.

Methods: Some 1000 subjects (> 65 years) were recruited in Kaniyambadi Block, Vellore, India, using a one-stage assessment procedure.

Results: The prevalence of dementia by Diagnostic and Statistical Manual IV standard, the Community Screening instrument for Dementia DF Score, the education adjusted 10/66 Dementia Research Group criteria, and the Geriatric Mental State was 0.8%, 6.2%, 10.6%, 63.2% respectively.

Conclusion: Differences in information, interview schedules, diagnostic criteria and settings contribute to variation in identification of people with dementia. Minor variations in criteria have a significant impact on diagnosis. The assessment of the clinical state is influenced by education, level of baseline function, impairment in current functioning, life style and demands on the person, tolerance of impairment and expectation by relatives and by differences between patients attending hospitals and those living in the community. The variation in rates demands a debate on the criteria for dementia in the community in general and for less literate populations in particular.