The authors examined the relation of early life socioeconomic status to incident Alzheimer's disease (AD), level of cognition and rate of cognitive decline in old age. For up to 10 years, 859 older Catholic clergy members without dementia at baseline completed annual clinical evaluations as part of the Religious Orders Study. The evaluations included clinical classification of AD and detailed cognitive testing. At baseline, indicators of early life household socioeconomic level (e.g., parental education) and the county of birth were ascertained. Socioeconomic features of the birth county (e.g., literacy rate) were estimated with data from the 1920 US Census. Composite measures of early life household and community socioeconomic level were developed. In analyses that controlled for age, sex and education, higher household and community socioeconomic levels in early life were associated with higher level of cognition in late life but not with risk of AD or rate of cognitive decline. The results suggest that early life socioeconomic level is related to level of cognition in late life but not to rate of cognitive decline or risk of AD.