Background. The apolipoprotein E (ApoE) epsilon 4 allele is associated with an increased risk of senile and probably presenile Alzheimer's disease. It is not yet clear whether the epsilon 4 allele also influences the duration/rate of progress of illness and the severity of the dementia. Method. We have retrospectively examined a series of ApoE genotyped presenile and senile autopsy cases of Alzheimer's disease (AD) for length of illness and severity of pathology. Results. We find no evidence that ApoE genotype affects the rate of progress of AD, but the degree of pathology at death may be increased. Conclusion. It appears that the rate of progress of AD as a whole is independent of the ApoE genotype.