Publisher Summary This chapter discusses the epidemiology, clinical features, diagnosis, pathology, and management of dementia associated with Parkinson's disease (PD). It also highlights the areas of deficiency related to PD and the relationship between Parkinson's disease (PD) dementia and dementia with Lewy bodies (DLB). Parkinson's disease dementia (PDD) is a common complication, affecting 80% of patients with PD during the course of their illness. Neuropsychiatric features, which may dominate clinical presentation and therapeutic prioritization, are an invariable feature of this dementia syndrome. Predictive risk factors involved in PDD are also discussed. The loss of dopaminergic innervation of the caudate nucleus and functional deafferentation of the dorsolateral prefrontal cortex may produce cognitive deficits in PD sufficient to qualify for mild cognitive impairment (MCI). Impaired attention and executive and visuospatial dysfunction are prominent in PDD. Behavioral and neuropsychiatric disturbances, termed “neuropsychiatric symptoms,” are extremely common in PDD and frequently predate the onset of dementia. The diagnosis of dementia is based on the presence of deficits in at least two of four core cognitive domains—attention, memory, executive, and visuospatial functions. The clinical diagnostic criteria for levels of “probable” and “possible” PDD are proposed. The guidelines for diagnosis of PDD are presented. Dementia and its predictors are investigated through screening blood tests, structural magnetic resonance imaging, single photon emission computed tomography and positron emission tomography, genetic predictors, and other biomarker measures.