We examined 510 subjects representing 83.2% of all citizens of a Finnish city aged 85 years or over. Mini-Mental State Examination (MMSE) scores, diagnosis of dementia by DSM-III-R criteria, and Apo-E genotype were determined. The prevalence of dementia was 38.6%. The odds ratio (OR) of the Apo-E epsilon4 carriers (with the reference population of people with the genotype epsilon3/epsilon3) for dementia was 2.36 (95% CI 1.58 - 3.53). There was a significant sex difference: The OR in women was 3.23 (95% CI 2.02 - 5.17) whereas among men it was insignificant. The mean MMSE score (+/- SD) among the Apo-E epsilon4 carriers (15.0 +/- 10.0) and noncarriers (18.7 8.6) (p