The effectiveness of an informant interview as a screening and assessment instrument for dementia was evaluated in a community survey of 398 people aged 78 or over. Participants received a battery of neuropsychological tests and were diagnosed for dementia by Diagnostic and Statistical Manual of Mental Disorders, 4th ed. (DSM-IV; American Psychiatric Association, 1994) criteria. Informants were independently interviewed about changes in everyday cognitive functioning over the previous five years. A factor analysis of the 31 items from the informant interview showed a large general factor. A long 31-item scale was constructed, as well as a short 12-item scale. The long scale had a sensitivity of 89% and a specificity of 89% for detecting dementia, while the short scale had a sensitivity of 83% and a specificity of 87%. Correlations with subtests of the neuropsychological battery ranged between .4 and .7. The informant scales were less affected by premorbid ability and education than was the Mini-Mental State Examination (MMSE).