This study examined the independent contributions of executive control function, general cognition, age, education, and medication usage to the comprehension of medical information. Randomly selected elderly retirees (N = 105) more than 70 years of age completed the Executive Interview (EXIT25), the Mini-Mental State Exam (MMSE), and the Hopkins Competency Assessment Test (HCAT). Cognitive measures were stronger predictors of HCAT scores than age, education, or number of prescribed medications. A discriminant model based on EXIT25 and MMSE scores correctly classified 91% of subjects relative to their HCAT scores. It was concluded that executive impairment is strongly associated with impaired comprehension of medical information. As many as 88% of probable Alzheimer's disease patients, 69% of institutionalized elderly retirees, and 49% of noninstitutionalized retirees may be impaired in their ability to comprehend medical information, even when it has been presented well below their educational level.