Parkinson's disease is a complex disorder in which the genetic aspects are only just being realized. The underlying cause for the degeneration of dopaminergic substantia nigra neurons and the formation of Lewy bodies in Parkinson's disease is unknown. The identification of clear inherited forms of the disease has provided important clues as to how this complex process may be occurring. Mutations have now been identified in the alpha-synuclein (4q21.3-23), parkin (6q25.2-27), and ubiquitin carboxy terminal hydrolase-L1 (4p16.3) genes in families with Parkinson's disease. Four additional chromosomal locations; 2p13, 4p14-15, 1p35-36, and 12p11.2-q13.1 have been linked to Parkinson's disease families but no pathologic gene mutations have been identified to date. As additional Parkinson's disease loci are mapped and their genes identified we will continue to add to our understating of the critical biochemical pathways involved and be able to develop effective disease altering treatments.