Seventy-eight hospital patients, 50 years of age or older, were selected for suspected changes in mentation and for the absence of focal or other organic brain disease. They were studied in relation to education, age, cerebral atrophy (by computerized tomography), electroencephalographic (EEG) slowing, and performance in several neuropsychologic tests. Adequate test-retest reliability of the cognitive measures and interjudge reliability of the cerebral atrophy and EEG measures were demonstrated. Stepwise multiple regression analyses suggested the following: (1) EEG slowing is the strongest and most general pathologic influence on cognition in elderly persons without overt brain disease. (2) Cerebral atrophy independently affects primarily the verbal recall of recent and remote information. (3) Age independently affects primarily recent memory for both verbal and nonverbal material. (4) Formal education is a powerful influence that must be accounted for in all studies of the effects of age on cognition.