The association between apolipoproteins and neurodegeneration is unclear. The authors examined the association of dementia with serum levels of apolipoprotein A-I (ApoA-I) alone and in combination with the apolipoprotein E genotype (ApoE). Subjects were Japanese-American men in Hawaii followed since 1965 in the Honolulu Heart Program cohort and the Honolulu-Asia Aging Study. Lipid levels were assessed in 1980-1982. Dementia was diagnosed in 1991-1993, 1994-1996, and 1997-1999 by using a multistep procedure and international guidelines. The sample consisted of 929 men (107 dementia cases). The relation between ApoA-I and dementia was examined by using Cox proportional hazards models adjusted for age, education, and cardiovascular risk factors. Compared with men in the lowest quartile, men in the highest quartile of ApoA-I concentration had a significantly lower risk of dementia (hazard ratio = 0.25, 95% confidence interval: 0.08, 0.78). Compared with men with both risk factors, those with a high ApoA-I concentration and no ApoE epsilon4 had a significantly lower risk of dementia (hazard ratio = 0.21, 95% confidence interval: 0.08, 0.52). Previous work has demonstrated an inverse relation between ApoA-I and cardiovascular disease, and the authors extended these findings to the risk of dementia. These results raise the possibility that different lipoprotein components of cholesterol may be differentially associated with dementia.