Apolipoprotein E (ApoE) allele frequencies were examined in a population-based sample (n = 475: age range 65-84 years: Amsterdam Study of the Elderly). The relation of ApoE epsilon 4 with dementia and with various types of late-life depression was studied. Depression was measured with the Geriatric Mental State schedule. Dementia was diagnosed by DSM-III-R criteria. It was expected that ApoE epsilon 4 allele frequencies would be elevated not only in Alzheimer's disease and dementia in general, but also in first episode, late-life depression accompanied by subtle cognitive impairment (possibly organic depression). However, the results indicated that epsilon 4 allele frequency is related to (family history of) dementia and cognitive impairment, but not to possibly organic depression. The main predictor of late-life depression is an episode of psychiatric problems before the age of 65 years.