This chapter discusses the recent neuroimaging studies that have started to unravel some of the mysteries behind the behavior and cognitive manifestations of Parkinson's disease (PD). In-vivo anatomical and functional confirmation of the cortico-striatal loops in humans comes from magnetic resonance imaging (MRI) techniques. In the early stages of PD, frontal lobe dysfunction most likely reflects deafferentation in relation to dopamine deficiency. In keeping with neuropathological studies, which have demonstrated Lewy bodies and cell loss in medial temporal lobe areas high-resolution MRI images have demonstrated hippocampal atrophy in PD. There is pathological and in-vivo positron emission tomography (PET) evidence that other neurotransmitters, particularly cholinergic pathways, are involved in PD dementia (PDD). In-vivo PET studies are currently investigating whether concomitant amyloid pathology may contribute to dementia in PD subjects, although at this point, it appears that amyloid deposition is associated more with dementia with Lewy bodies (DLB) than with PDD.