What causes Parkinson's disease is largely unknown but both environmental factors and genetic risk factors play a role. Over the years researchers have identified mutations in genes that are responsible for the disease in families and these findings have helped researchers tremendously in their research to understand the disease process. However, familial forms of Parkinson's disease represents only a small minority of patients and it is therefore important to understand the genetic influences on the more common forms of the disease. This work is however very complex and progress has therefore been very slow. We propose to search for genetic factors in genetically isolated populations because in these populations the pattern of genetic influences is less complex. We have identified several populations that are suitable for this purpose. For two of these we have already ascertained all patients with the disease and propose to perform a genetic screen in order to identify genetic risk factors. We have also identified additional population for which patients still need to be collected. This population will be used for replication of our results and in combination with a cohort of patients from the general population will be used to confirm that our findings are of importance for the general population.