OBJECTIVE: To compare magnetic resonance imaging (MRI) patterns of cortical thinning in subjects with dementia with Lewy bodies (DLB), Alzheimer's disease (AD), and normal aging and investigate the relationship between cortical thickness and clinical measures. METHODS: Study participants (31 DLB, 30 AD, and 33 healthy comparison subjects) underwent 3-Tesla T1-weighted MRI and completed clinical and cognitive assessments. We used the FreeSurfer analysis package to measure cortical thickness and investigated the patterns of cortical thinning across groups. RESULTS: Cortical thinning in AD was found predominantly in the temporal and parietal areas extending into the frontal lobes (N = 63, df = 59, t >3.3, p <0.005, FDR-corrected). In DLB, cortical thinning was less diffuse with focal areas of cortical change predominantly affecting posterior structures (inferior parietal, posterior cingulate, and fusiform gyrus) (N = 64, df = 60, t >3.6, p <0.005, FDR-corrected). The average reduction in cortical thickness in medial temporal lobe structures was less in DLB (6%-10%) than in AD (15%-24%), and similar to the reduction in cortical thickness observed in other regions including inferior parietal, precuneus, and posterior cingulate (6%-9%). Associations between cortical thickness and clinical measures (MMSE and verbal fluency) were also observed in DLB (N = 31, df = 27, t >2.8, p <0.01 uncorrected). CONCLUSION: Cortical thickness may be a sensitive measure for characterising gray matter loss in DLB and highlights important structural imaging differences between the conditions.