Inheritance of the apolipoprotein E (ApoE) epsilon 4 allele is a risk factor for Alzheimer's disease (AD) and is associated with increased deposition of beta-amyloid (A beta) in AD, Down's syndrome, and normal aging. A beta deposition in the form of senile plaques (SPs) has recently been described in patients with temporal lobe epilepsy (TLE). We studied the relationship between ApoE epsilon 4 genotype and the deposition of A beta in temporal lobe tissue from patients who underwent temporal lobectomy for intractable epilepsy. TLE patients with SPs had a 70% ApoE epsilon 4 carrier frequency compared with a 27% carrier frequency among age-matched TLE controls without SPs. Our data suggest that the association between ApoE epsilon 4 and intracerebral A beta accumulation is not unique to the elderly or to those with dementia, and may be a feature of conditions in which there is both an ApoE epsilon 4 allele and over-production of A beta precursor protein, and, presumably, A beta.