We examined the presence of cortical or subcortical brain atrophy (as shown by CT scans) in patients with Parkinson's disease (PD) and assessed whether there were significant correlations between CT measurements and the presence of cognitive deficits. There were three main findings. First, patients with bilateral symptoms of PD showed more severe cortical and subcortical atrophy than age-matched normal controls. Second, the presence of unilateral symptoms of PD was significantly associated with contralateral brain atrophy only in patients with right hemi-PD. Third, there was a significant correlation between neuropsychological deficits and atrophy in specific brain areas.