Executive SummaryThe most important advance toward understanding the disease came in 1817 with the publication of “Essay on the Shaking Palsy” by James Parkinson, a London surgeon. He was the first to identify the group of symptoms characteristic of Parkinson's disease.As the disease progresses, impairment worsens and eventually the patient is unable to get out of bed without assistance and is confined to a wheelchair. The mean age of onset is 58 years, and while the rate of disease progression varies from patient-topatient, the average interval from the initial signs of Parkinson's disease to late-stage disease is about 15 years.Although there have not been any absolute epidemiologic studies on Parkinson's disease, medical experts believe that up to 1 million Americans have Parkinson's disease; another 50,000 cases are diagnosed each year.A number of Parkinsonian symptoms are common enough to be known as the cardinal signs of the condition. All are primarily physical in nature, at least in the early stages of the disease, and include a resting tremor, rigidity, slowed movement and postural instability. One or more of these symptoms is always present in Parkinson's disease.Dementia is also associated with Parkinson's disease. Approximately 20% of the patient population suffers from some form of dementia, and most often this occurs in the later stages of the disease. It is important to keep in mind cognitive abnormalities are usually present in the Parkinson's disease patients, and the manifestation of these abnormalities can often be misdiagnosed as dementia.Levodopa and its combinations remain the most effective medication to relieve symptoms. As the disease progresses, rational polypharmacy (combination therapy) increasingly becomes necessary.