Assessment of cognitive functioning is an important component of telephone surveys of health. Previous cognitive telephone batteries have been limited in scope with a primary focus on dementia screening. The Brief Test of Adult Cognition by Telephone (BTACT) assesses multiple dimensions central for effective functioning across adulthood: episodic memory, working memory, reasoning, verbal fluency, and executive function. The BTACT is the first instrument that includes measures of processing speed, reaction time, and task-switching/inhibitory control for use over the telephone. We administered the battery to a national sample (N = 4,268), age 32 to 84 years, from the study of Midlife in the United States (MIDUS) and examined age, education, and sex differences; reliability; and factor structure. We found good evidence for construct validity with a subsample tested in person. Implications of the findings are considered for efficient neuropsychological assessment and monitoring changes in cognitive aging, for clinical and research applications by telephone or in person.