The adequacy with which brief cognitive tests suitable for telephone administration can assess cognitive decline due to aging and Alzheimer's disease is uncertain. The authors examined these issues with data from the Religious Orders Study, which involves annual clinical evaluations and brain donation at death. Participants are 996 older Catholic clergy members. Analyses focused on seven cognitive tests which can be administered in person or by telephone in less than 15 min. Composite measures of global cognition and of episodic, semantic and working memory were formed. During a mean of 5.8 years of follow-up, performance on each composite measure declined in persons with and without dementia at baseline. Among those without dementia, possession of the apolipoprotein E epsilon4 allele was associated with more rapid cognitive decline, especially in episodic and working memory. Level of performance on each cognitive measure proximate to death was inversely related to the level of cortical plaques and tangles in the brain. In a subset of persons who were given the tests by telephone, there was no evidence that performance differed from in-person administration. The results suggest that briefly assessing cognition with tests amenable to telephone administration may prove useful in longitudinal epidemiologic studies of older persons.