Parkinson s disease (PD) is the second most prevalent neurodegenerative disease, affecting more than 1 million elderly Americans. The causes of PD are largely unknown, but may include both genetic and environmental factors. We thus propose a large study to investigate the roles of diet, lifestyle, genes and their potential interactions in PD etiology, using the NIH-AARP Diet and Health Study. The AARP cohort was established by investigators at NCI and recruited over half a million participants in 1995 and had prospectively collected detailed information on diet and lifestyle. At baseline, participants were 50 years or older and included 40% women. After more than 8 years of follow-up, we expect to confirm 1,208 incident PD cases with their neurologists. We will comprehensively examine the associations between diet and lifestyle and risk of PD, focusing on dietary antioxidants, fat, caffeine, dairy products, estrogen use, obesity, physical activity, and non steroidal anti-inflammatory drugs (NSAIDs). Further, we will collect saliva samples from PD patients and selected controls without PD for genetic analysis. These results will be used to explore the PD associations with several common genetic polymorphisms and, for the first time, their interactions with several promising diet or lifestyle exposures. Many of the specific aims are novel and important but have been rarely examined in previous investigations. The findings will improve our understanding of the complex relationships among diet, lifestyle, gene-environment interaction, and PD etiology and may potentially contribute to successful PD prevention strategies.