Summary The pathology of Parkinson's disease (PD) is characterized by the presence of neuronal loss, Lewy bodies (LBs), and Lewy neurites (LNs) at predilection sites in the nervous system. During the course of PD a characteristic pattern of lesions develops in both the central and peripheral nervous system, with a predominant involvement of ‘efferent’ subcortical structures such as the substantia nigra and amygdala. ‘Afferent’ cortical structures such as the entorhinal region are frequently involved in Alzheimer-type pathology. In this chapter the clinical features and postmortem findings of 33 patients with PD are reviewed and compared, with special attention being paid to the frequent but not exclusive association of LBs/LNs with Alzheimer-type pathology. Although a clear relationship between the neuropathological findings and the clinical features of psychopathology and/or dementia could not be observed, one could speculate that the Parkinson-specific lesions in cortical and subcortical structures and the Alzheimer-type pathology, which is seen most often in the entorhinal region, reinforce each other and thus are responsible for the development of dementia in PD. CA2 ubiquitin-immunoreactive neurites were found in almost all patients with PD and should be considered a normal finding in PD, irrespective of whether or not the patient is demented. Introduction Thirty-three patients with a clinical history of Parkinson's disease (PD), with or without concomitant affective, behavioral, and/or cognitive changes were assessed. They were referred to the Department of Neurology of the Medisch Spectrum Twente, The Netherlands, to determine the relationship, if any, between clinical PD with or without dementia and neuropathological changes.