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 ε4 carriers (with the reference population of people with the genotype ε3/ε3) for dementia was 2.36 (95% CI 1.58–3.58). 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 ε4 carriers (15.0 ± 10.0) and noncarriers (18.7 ± 8.6) (p < .001) differed among the whole population, but not within the demented or nondemented subjects analyzed separately. This study does not support the hypothesis that the Apo-E ε4 allele impairs cognitive functions of nondemented elderly, at least in those surviving to very old age.