The relationship between extrapyramidal sign (EPS) severity and cognitive function was investigated in 184 patients with idiopathic Parkinson's disease (PD) and 301 normal elderly individuals from a community-dwelling cohort in northern Manhattan, New York City. Fifty-six of the patients with PD met criteria for dementia of the Diagnostic and Statistical Manual of Mental Disorders, third edition, revised, and of the National Institute of Neurological and Communicative Disorders and Stroke-Alzheimer's Disease and Related Disorders Association. EPS were rated according to the Unified Parkinson's Disease Rating Scale. Cognitive function was assessed by neuropsychological tests of memory, orientation, abstract reasoning, language, construction, and psychomotor speed. Significant associations were found between EPS and neuropsychological performance in PD patients without dementia. Yet EPS severity was unable to account for the pronounced cognitive impairment in PD dementia. Individuals in the normal group with subtle EPS, but without overt idiopathic PD, showed widespread cognitive changes, including impairment in most of the tests that differentiated PD patients from normal subjects. Prospective follow-up of these individuals will determine whether this represents a preclinical stage of PD or constitutes an early manifestation of dementia.