Cognitive impairment is very common in patients with Parkinson s disease (PD). Brain changes accompanying cognitive decline in PD are still not fully established. Methods: We applied cortical pattern matching and cortical thickness analyses to the three-dimensional T1-weighted brain MRI scans of 14 age-matched cognitively normal elderly (NC), 12 cognitively normal PD (PDC), and 11 PD dementia (PDD) subjects. We used linear regression models to investigate the effect of diagnosis on cortical thickness. All maps were adjusted for multiple comparisons using permutation testing with a threshold p <0.01. Results: PDD showed significantly thinner bilateral sensorimotor, perisylvian, lateral parietal, as well as right posterior cingulate, parieto-occipital, inferior temporal and lateral frontal cortices relative to NC (left pcorrected = 0.06, right pcorrected = 0.009). PDD showed significantly thinner bilateral sensorimotor, right frontal and right parietal-occipital cortices relative to PDC (right pcorrected = 0.05). The absolute difference in cortical thickness between PDD and the other diagnostic groups ranged from 3 to 19 . Conclusion: Our data shows that cognitive decline in PD is associated with cortical atrophy. PDD subjects have the most widespread gray matter atrophy suggesting more cortical involvement as PD patients progress to dementia. ? 2013-IOS Press and the authors. All rights reserved.