Parkinson's disease (PD) is a progressive neurodegenerative disorder that affects 1 million people in the United States. Although the cause of PD remains unknown, a number of factors that increase the risk of developing this disease have been identified. Other factors that may prevent or slow down PD development and progression have also been found. In this review, we describe current basic, clinical and epidemiological findings on risk and neuroprotective factors and discuss how they can affect PD.