We determined the apolipoprotein E4 (apoE) genotype in 12 cases of autopsy-confirmed hippocampal sclerosis dementia (HSD), a disorder characterized pathologically by neuronal degeneration, predominantly of temporal lobe structures, without senile plaques or neurofibrillary tangles. The frequency of the apoE4 allele in HSD was 12.5%, similar to that of a control population and significantly different from the approximately 40% found in Alzheimer's disease (AD) (P < 0.001). These observations suggest that apoE4 is not a risk factor for HSD.