Objective. Naturalistic measures of prospective memory (PM) show less age-related decline than laboratory measures. We investigated whether a naturalistic measure of PM differentiates between normal ageing, mild cognitive impairment (MCI), and dementia.

Method. Ninety-eight older adults agreed to perform a time-based PM task in their everyday lives.

Results. Despite a self-selection bias in task acceptance, dementia participants performed more poorly relative to both the MCI and control group. Performance on the naturalistic PM task showed good convergent validity with both a cognitive screening measure and a laboratory PM assessment.

Conclusions. PM difficulties are experienced in the everyday lives of people with dementia and are related to laboratory-based assessments but do not appear to be evident on a naturalistic task for those with MCI.