Mild cognitive impairment (MCI) is a heterogeneous clinical syndrome defined as evidence of cognitive decline which is greater than expected for an individual’s age and educational level but which does not significantly impact on activities of daily living. The challenge for clinicians is to distinguish between normal cognition, cognitive decline normal for ageing, subjective cognitive decline, delirium, MCI and dementia. The history should focus on the onset and progression of symptoms. An acute or fluctuating course suggests delirium or another potentially reversible cause.