In addition to memory impairment, deficits in other cognitive processes are common in the advanced stages of Alzheimer's disease (AD). The diagnosis of AD does not consider the relative prevalence of deficits in cognitive areas other than memory. We report on the prevalence of aphasia, apraxia, and other cognitive changes in individuals from a large representative sample of elderly Canadians. The proportion of these symptoms and the relevant neuropsychological test performance were compared in a group of 749 people over 65 years in age with AD and a control group of 563 people without cognitive impairment. Agnosia was less common in both groups than were deficits in complex visuomotor tasks, abstract thinking. aphasia, and constructional defects. The occurrence of all symptoms increased, and levels of performance on relevant neuropsychological tests decreased, with severity of Alzheimer disease. The tests did not, however, distinguish between possible and probable AD. Both these diagnostic groups showed similar levels of performance, which suggests that this distinction is not clinically meaningful.