The aim of our study was to establish the contribution of distinct pathological aggregates (cortical Lewy bodies (LB), neuronal tau-inclusions and β-amyloid plaque (Aβ) deposition) in dementia related to Parkinson's disease (PD) in a large autopsy cohort. We studied the brains of 155 PD patients, 109 of whom were clinically demented. The total LB score, the Braak stages for neurofibrillary tangles (NFT) and the Thal phases for Aβ deposition were assessed in each case, according to previously published guidelines. All the three lesion types were more abundant in the demented PD group, compared to the non-demented PD group, but neocortical LB pathology was the most important substrate of dementia. A significant correlation was found between the severity of Aβ phases, NFT stages and cortical LB scores. In a subgroup of severely demented PD patients, cortical tau burden was much higher than in the rest of the group. Extensive cortical NFTs associate unavoidably with dementia. Some patients remain cognitively intact despite high cortical LB score. In conclusion, our data strongly support a combining, yet distinct role of neocortical LBs and tau deposits.