Patients with late paraphrenia or late onset schizophrenia frequently have associated cognitive impairment which may in some cases progress to a recognized dementia. The frequency of the apoE ϵ4 allele is high in individuals who develop Alzheimer's disease. Twenty-three patients with late paraphrenia were genotyped for ApoE. The frequency of the ϵ4 allele was comparable with that found in a large group of centenarians, but lower than previously reported from populations of normal controls and Alzheimer's disease patients. Two out of three male patients tested had the rare ϵ2/ϵ2 genotype, which was not found in any of the females.