The causes of Parkinson’s disease (PD), the second most common neurodegenerative disorder, are still largely
unknown. Current thinking is that major gene mutations cause only a small proportion of all cases and that in most
cases, non-genetic factors play a part, probably in interaction with susceptibility genes. Numerous epidemiological
studies have been done to identify such non-genetic risk factors, but most were small and methodologically limited.
Larger, well-designed prospective cohort studies have only recently reached a stage at which they have enough incident
patients and person-years of follow-up to investigate possible risk factors and their interactions. In this article, we
review what is known about the prevalence, incidence, risk factors, and prognosis of PD from epidemiological
studies.