General practice patients aged 75 years and over were screened for cognitive impairment using the Mini-Mental State Examination. Those scoring 23 or below and a sample of those scoring 24 or 25 were assessed using the Cambridge Mental Disorders of the Elderly Examination (CAMDEX), a structured interview schedule specifically designed to detect mild dementia. The CAMDEX includes a mental state examination, a psychiatric history, detailed cognitive testing and an information interview. The prevalence of dementia in 2311 patients was found to be 10.5%, about half that found in most earlier studies. Possible reasons for this low rate are discussed.