Parkinson’s Disease is an ailment affecting primarily the elderly, with the majority of patients diagnosed at 60 years of age or older. Yet, the clini- cal and pathological features of the disease may oc- cur in younger individuals. Younger-onset Parkin- son’s is a diagnosis for individuals ages 20-39 years of age. Whether younger-onset Parkinson's Disease is truly the same illness as that of older individuals is not known. Parkinson’s Disease affects about 1 in 100 Americans over the age of 60 years. The illness is much rarer at younger ages. The exact number of cases in younger individuals is difficult to estimate. It is said that of patients seen in clinics in the United States, about 5% have their initial symptoms before age 40 years. The number of young-onset PD cases in Japan may be twice as great as the number in the United States; however, the reason for this geo- graphic difference is unknown.