We determined apolipoprotein E (ApoE) genotypes in 122 autopsied demented patients. The frequency of the ApoE ϵ4 allele was 39.6% in Alzheimer's disease (AD), 29.0% in the Lewy body variant of AD (LBV), and 6.25% in diffuse Lewy body disease. For AD and LBV patients, the e4 frequency was significantly higher than that reported in nondement-ed controls (10 to 15%). Therefore, LBV and AD share ApoE ϵ4 as a genetic risk factor, providing further evidence that these conditions overlap.