The etiology and pathogenesis of Parkinson’s disease have remained a mystery since the first description of the disease, but the neuropathology of the disorder, as we now know it, is fairly simple and straightforward. The most important lesion is in the substantia nigra pars compacta, where nerve cells degenerate together with their nigro-striatal fiber tract, causing a severe depletion of dopamine in the basal ganglia.