Additional epidemiologic studies may provide important insights into the etiology of Parkinson's disease. Moreover as the elderly population of Europe and the United States grows, accurate public health planning requires accurate incidence and prevalence estimates. The recent development of a therapy that may slow disease progression (see article by Tetrud elsewhere in this issue) makes early identification and treatment of Parkinson's disease particularly important. Investigations of early markers of Parkinson's disease or markers of disease susceptibility are critical areas of future research, requiring careful collaboration between epidemiologists and laboratory scientists.