BACKGROUND: Symptoms of memory loss are very common with estimated prevalence between 22% and 50% in those older than 65 years of age. Those with symptoms of memory loss and impaired performance on memory tests are at high risk of progression to Alzheimer disease. The relative importance of different aspects of the clinical history in predicting cognitive impairment is uncertain. METHODS: Fifty-six patients with symptoms of memory loss were recruited from the National Hospital for Neurology and Neurosurgery. A clinician recorded type and duration of memory symptoms as perceived by the patient and their informant, and use of memory aids. All patients subsequently underwent magnetic resonance imaging (MRI) and neuropsychologic testing. FINDINGS: (i) Informant, but not patient, ratings of memory were associated with performance on tests of memory function and with hippocampal size on MRI. (ii) Decreased use of memory aids and shorter duration of memory symptoms were more common in those with memory impairment. INTERPRETATION: In a clinical setting, information gathered from the history was associated with cognitive impairment on memory testing and brain appearances on MRI. The history from a close informant is particularly important being more strongly predictive of cognitive impairment (P=0.0002) than subjective symptoms, use of memory aids or duration of symptoms.