Seven dextral patients with Parkinson's disease (PD) who had predominant right-sided motor signs were compared on neuropsychological tests with eight dextral patients with PD who had predominant left-sided signs. Objective criteria for group designation were developed from clinical ratings. The patient subgroups were matched on age, education, estimated premorbid IQ, severity of motor signs, and medication usage. Patients with signs lateralized to the right were more impaired on tests of dominant hemisphere function (serial digit learning, confrontation naming, and verbal associative fluency), but no differences were found on tests of nondominant hemisphere function (form sequence learning, line orientation, facial recognition), indicating some correlation of neuropsychological performance with lateralization of predominant motor signs. Findings demonstrate that the cognitive deficits (particularly visuospatial) previously reported in the literature are not seen consistently in all subjects with PD.