Disproportionate involvement of language has been claimed to be a distinguishing feature of Alzheimer's disease (AD) with onset before age 65. We tested this hypothesis in a group of 133 patients with possible AD by NINCDS criteria. Sixty-one had onset of symptoms prior to age 65; the remaining 72, at 65 or later. The two groups were well matched on overall dementia severity as measured by the Mini-Mental State Exam. Using standardized tests, we did not find any significant differences in the severity of language dysfunction between the two groups, particularly after controlling for greater attention/concentration deficits in the early-onset group. Previous reports of differences in language dysfunction between early- and late-onset AD may have been due to small sample sizes and nonstandardized testing.