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There are about 2,5 million people with multiple sclerosis worldwide. In the Czech Republic, the number of people with MS is estimated to be about 25,000. In the recent years, there have been 700 new cases diagnosed every year. 

Evidently, such increase is due not only to the availability of better diagnostic tools and methods but also to a higher incidence of autoimmune diseases in developed countries in general.

Multiple sclerosis is more common in women and in Indo-European population. Prevalence in population (incidence per 100,000 people) is about 1%. If there is a case of multiple sclerosis in the family, the probability raises to 3-4%. If one of identical twins gets the disease, the other has approximately 30-40% chance of getting it as well. It follows that besides genetics, also the environment is very important. Epstein-Barr virus (EBV), smoking, and deficiency in vitamin D are considered risk factors for MS. Last factor mentioned explains why MS is more common towards the poles and why the lowest prevalence is in people that live near the equator. Recently, it has been discovered that obesity may be one of the risk factors for multiple sclerosis, especially in teenagers. Probably, this is connected with inflammatory function of leptin which is secreted by fat cells.

Multiple sclerosis is mainly a disease of young adults. The most frequent incidence of first symptoms of the disease is in the relapsing-remitting multiple sclerosis (RR-MS) form between 20 and 40 years. However, the MS can evolve without being noticed for a longer period of time. More and more frequently it is being diagnosed in children and adolescents. For the second one, there are well documented cases with first symptoms in the sixth or seventh decade of life. In average MS is two to three times more common in women than in men, suggesting that hormones may also have an impact on immune system.

Primary progressive multiple sclerosis (PP MS) is the least common form of MS that affects approximately 10-15% of people with MS. The numbers of women and men affected are approximately equal. PP MS is usually diagnosed in older individuals between the ages of 40 to 50. Yet, there are rare familiar cases of PP MS when the first symptoms appear before the patient reaches the age of 40.

Incidence of MS varies depending on the population and geographic area. Most often MS affects the Indo-European population of the temperate climate of the northern hemisphere. The number of patients increases hand in hand with the distance from equator. Minimal incidence is close to the equator, and its increase in connection with raising latitude is due to the amount of sunshine, and the influence of vitamin D on immune system. However, data concerning incidence, can vary significantly in one geographic area where both latitude and climate should be similar and relatively steady. Again, such differences suggest that, geographical factors are only a part of a complex mosaic.

Most often MS develops in white race population (especially people originally from Northern Europe). The prevalence of the disease in other ethnic groups is lower. Regardless their latitude, there are certain population groups that are almost untouched by MS – e.g. Eskimos, Hungarian gypsies, Laplanders, Australian aborigines, or Maori in New Zealand. Also migration from one geographic area to another could influence the risk of MS development. Migration studies show that if a person after his 15th year of age moves from a country with a high risk of MS to a country with a low risk, he brings along the risk of the country where he grew up.

The same is valid the other way around. In accordance with the basic theory of complex interactions of genetic and environmental factors necessary for the development of MS, these studies support the opinion that there is a certain external launching effect working in the first years of life. Probably, given external conditions, such effect is able to induce the disease in genetically equipped individuals.