Worldwide, based on the available prevalence studies, there are likely to be more than 6 million people with Parkinson's Disease. However, due to so many people with Parkinson's Disease remaining undiagnosed, there may be millions more. In China alone there are more than 1.7 million people with Parkinson's Disease.

The world's highest prevalence of Parkinson's Disease of any region is in Nebraska, U.S.A. with 329.3 people per 100,000 population. It is possible that there is  a very high  prevalence of Parkinson's Disease in Nebraska due to the heavy use of insecticides in what is largely a farming area. The U.S.A. is the country as a whole with the world's highest prevalence of Parkinson's Disease. The U.S.A. has a high life expectancy that would enable a larger number of people with Parkinson's Disease, but it is also easier to be diagnosed with a medical disorder in the U.S.A..

The Parsi community of Mumbai, India have a prevalence of Parkinson's Disease of 328.3 per 100,000 population, which is almost in excess of that found in Nebraska. This is despite India as a whole having a low prevalence. The Parsi practice Zoroastrianism, a religion based on the teachings of Zoroaster. As part of their religion, the Parsis burn Aspand seeds to rid their children of the Evil Eye, which is the name for a sickness transmitted by someone who is envious, jealous, or covetous. The fumes are often inhaled. Aspand seed is the richest natural source of two alkaloids, harmine and harmaline. They are a type of drug known as MAO Inhibitors, which are also used in Parkinson's Disease. Long term use of MAO inhibitors, eventually has the opposite effect, and so may cause the high prevalence of Parkinson's Disease amongst the Parsi.

The prevalence for each country  per 100,000 of population, in those countries in which it is known,  from highest to lowest is : U.S.A. 329-107, San Marino 185, Faeroe Islands 206-183, Germany 183, Spain 170-122, Italy 168-104, Finland 166-120, Bulgaria 164-137, Estonia 152, Australia 146-104, England 139-121, Portugal 135, Cuba 135, Canada 125, China 119-57, Scotland 103, Norway 102, Japan 99 - 76, Sweden 76, New Zealand 76, Nigeria 67, Bolivia 50, Libya 31, Colombia 31, Tanzania 20, Korea 19, Ethiopia 7. The prevalence differs from country to country and can even differ within countries. The prevalence amongst Bulgarian Gypsies is only one tenth of that found amongst other Bulgarians. The prevalence in the U.S.A. tends to differ according to race, with Hispanics, then Whites, then Asians, then Blacks being more prone. However, other studies have given different results.

AGE DISTRIBUTION

In 1875, Henri Huchard (1844-1911) detailed the first case of Juvenile Parkinson's Disease. He described a 3 year old child who had all the clinical features of Parkinson's Disease. The youngest reported case of Parkinson's Disease since then is that of a 10 year old girl from Okalahoma, who showed her first symptoms of Parkinson's Disease at only 2 years old. However, it is very uncommon for people under the age of 30 to develop Parkinson's Disease. Parkinson's Disease usually occurs when people are significantly older than that and becomes increasingly more common with age. The average age at which symptoms usually begin differs from county to country, with the oldest average onset being in Sweden 65.6, and Estonia 66.9. However, Parkinson's Disease does not become progressively more likely with age, because amongst the very oldest of people (those between 110 and 119 years old) Parkinson's Disease is very uncommon.

The rate at which people with Parkinson's Disease are newly diagnosed differs greatly according to the country. The incidence for each country, in which it is known, per 100,000 of population per year from highest to lowest is : Faeroe Islands 21.1, U.S.A. 20.5-13.0, Japan 16.9 - 10.2, Estonia 16.8, Finland 16.6-14.9, England 12, Netherlands 11.5, Italy 10.1, Sweden 7.9, Libya 4.5.