This study will examine the roles of diet, lifestyle, genes, and their possible interactions in the cause of Parkinson's disease, using information from the NIH-AARP Diet and Health Study. The NIH-AARP study was established in 1995 to examine the roles of diet and lifestyle in cancer. It included 567,169 AARP members 50 or older from California, Florida, North Carolina, Pennsylvania, New Jersey, Louisiana, and the Atlanta and Detroit metropolitan areas. In 1995, participants completed a comprehensive questionnaire on diet and a survey on demographics, medications, as well as a follow-up survey in 1996 with more detailed questions on lifestyle and medications, as well as cooking methods and early life dietary habits. A third followup survey is currently underway.