The past few years, mutations in 5 genes (a-synuclein, parkin, DJ-1, PINK1, and LRRK2) have been firmly implicated, and additional chromosomal loci have been mapped for inherited forms of Parkinson's disease (PD). These discoveries have profound implications for both the scientific and clinical communities. First, although some of the Mendelian forms of PD are very rare (including those caused by alfa-synuclein, DJ-1, and PINK1 mutations) they are facilitating greatly the dissection of the molecular pathways that lead to death of dopaminergic neurons; these pathways might also be implicated in the pathogenesis of the common forms of PD. Second, the discoveries of Mendelian forms are challenging the concept of PD as one disease, as well as the validity of the current clinico-pathological disease definition. Last, mutations in 2 of these genes turned out to be frequent enough to have relevance in clinical practice: parkin mutations are common in early-onset familial and sporadic PD; moreover, emerging data delineate mutations in the LRRK2 gene (encoding the dardarin protein) as a frequent cause of the familial late onset PD forms, and even of few late-onset sporadic cases. The importance of genetic testing is expected to increase in the near future in the PD field. Here, the author provides a brief update on the genetics of the monogenic forms of PD.