The question of whether Parkinson's disease (PD) patients who have left (LPD) or right (RPD) motor predominance also exhibit cognitive differences is controversial. We examined this issue using a neuropsychological battery designed to provide a balanced sampling of both right- and left-hemispheric functions. RPD patients were impaired relative to LPD patients on verbally mediated tasks (left hemisphere function), but there was no group difference for visuospatial tasks (right-hemispheric function). In addition, there was a significant correlation between the extent of right side motor predominance and performance on verbal tasks, but there was no relationship between left side motor symptoms and performance on visuospatial tasks. The controversy related to cognitive differences in hemiparkinsonism may be due to the balance of the assessment procedure, the severity of motor asymmetry, or both.