The genetic basis of many monogenic neurological diseases with parkinsonian features has been elucidated over the past few years. The clinical and genetic features are discussed for the diseases with prominent parkinsonian signs. There is also accumulating evidence for a role of genetic factors in the aetiology of idiopathic Parkinson's disease (PD); however, the approach to polygenic diseases is quite different from that to the simpler single-gene disorders. The role of epidemiology in not only establishing genetic susceptibility, but its impact on estimating the size of the problem, is also discussed. A number of candidate genes have been studied in PD but, to date, there is no conclusive proof for any of these. It therefore seems likely that a random genome search is required, and the technical and statistical methods are now available. It is hoped that knowledge of the genes involved will lead to better therapy for this incurable and common disorder.