Abstract
This paper presents a detailed review of the literature related to the mental status of patients with Parkinson Disease (PD). Even though Parkinson stated that the intellect remains intact, several authors have shown that dementia is found in a sizeable percentage of patients with PD. Several papers written after 1970 suggest that this percentage is between 40 and 50. Both neuropsychological and neuropathological data indicate that the majority of demented PD patients show findings indistinguishable from Alzheimer Disease (AD). This finding is not related to aging and remains unexplained, even though it has been suggested that this mental status change may be related to dopaminergic drugs.