We examined the existence of a relationship between polymorphism and dementia in subjects aged 90 years and above. The sample included 732 unrelated Chinese nonagenarians/centenarians (aged 90-108 years, mean age 93.68 years; 67.5% women). The Pro12Ala variant was examined using polymerase chain reaction restriction fragment length polymorphism. Cognitive function was measured with 30-item mini-mental state examination. The genotype frequencies of the Pro12Ala polymorphism were 0% Ala12Ala, 9.1% Pro12Ala, and 90.9% Pro12Pro. The prevalence rates of dementia were 64.9% in the whole sample (45.0% for men and 74.5% for women). In both men and women, between subjects with and without 12Ala carriers, there was no significant difference in cognitive function scores and also no significant difference in prevalence of dementia; there was no significant difference in frequency of 12Ala carriers between subjects with and without dementia. Multiple logistic regression was performed by adjusting clinical factors that are thought to be associated with cognitive function or with 12Ala carriers. We found that 12Ala is not a risk factor for dementia. We found that Pro12Ala polymorphism in PPAR-gamma2 was not directly correlated with dementia among Chinese nonagenarians and centenarians.