More than 1 million people in the United States have Parkinson disease (PD), more than are diagnosed as having multiple sclerosis, amyotrophic lateral sclerosis, muscular dystrophy, and myasthenia gravis combined. PD affects approximately 1 in 100 Americans older than 60 years. It burdens patients, their care partners, and the overall healthcare system. This article reviews the epidemiology, clinical features, putative environmental risk and protective factors, neuropathological aspects, heterogeneity, medical management, and recent studies regarding genetics and PD. The article suggests that based on new research, the prevalence of PD varies in different regions of the United States. Some progress has been made in identifying the risk and protective factors of PD, and a newly emphasized area of study in PD is genetics. Patient care recommendations, based on American Academy of Neurology practice guidelines, are outlined to show the state of contemporary medical management of PD and related disorders.