There is a subset of very elderly patients with senile dementia in whom abundant neurofibrillary tangles are present, mainly in the hippocampal region, without a significant number of senile plaques. In a retrospective neuropathological examination of 239 dementia patients, 14 were found to have this type of senile dementia. The apolipoprotein E ϵ2, ϵ3, and ϵ4 allele frequencies in this patient group were 0.39, 0.50, and 0.11, respectively. Such a high frequency of the ϵ2 allele suggests that this type of dementia is distinct from Alzheimer's disease not only from a neuropathological but also from a genetic viewpoint.