The objective of this study was to determine the relationship between the presence of extrapyramidal signs and the severity of cognitive and functional impairment in patients with Alzheimer's disease (AD). Eleven university medical centers in the United States and France participated in the Consortium to Establish a Registry for Alzheimer's Disease (CERAD) study of extrapyramidal signs in AD. Forty-seven patients with probable AD who had extrapyramidal signs were matched by sex, race, education, and age with 132 probable AD patients without extrapyramidal signs. The main outcome measures were the Clinical Dementia Rating, Blessed Dementia Scale, and the CERAD Neuropsychology Battery (verbal fluency, naming, Mini-Mental State Examination, word list learning, word list recall, savings ratio, word list recognition, and constructional praxis). AD patients with extrapyramidal signs performed more poorly than AD patients without parkinsonism on various neuropsychological tests, even after controlling for the Clinical Dementia Rating and reported duration of cognitive impairment. The severity of the extrapyramidal manifestations was related to the degree of cognitive and functional impairment. Muscular rigidity and bradykinesia were the most frequent extrapyramidal signs associated with AD. Patients with AD associated with extrapyramidal signs have greater cognitive and functional impairment than AD patients without clinical evidence of parkinsonism.