MS is more common in women. Approximately twice to thrice as many women as men have MS, similar to female:male ratio seen in other autoimmune diseases.

It is unclear why women are more prone to autoimmune diseases but many think it is related to women hormonal cycle.

MS is more common in Caucasians.

According to the National Multiple Sclerosis Society, there are an estimated 1 Million, up from the 350,000-500,000 people estimated in the 1990s with MS in the United States. It is estimated that approximately 3.5 million people suffer with MS worldwide.

There is a very high prevalence of MS in northern Europeans countries, especially in Sweden, Norway, Denmark, and Iceland. Australia, the British Isles, Canada, Ireland, New Zealand, and the United States also have comparatively high prevalence rates. Conversely, prevalence rates are relatively lower in Africa, China, India, Japan, and Southeast Asia. In the diagram most common countries with MS are the dark brown and purple.