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MS Prevalence FAQs


Q: What is prevalence and how is it different from incidence?
A: Prevalence is the number of people living with a disease. Incidence is the number of people newly diagnosed with a disease within a given period of time.

Q: How many people are living with MS in the U.S. according to the new prevalence estimate?
A: Nearly 1 million people (913,925)

Q: How is the new estimate different than numbers used before?
A: More than twice as many people are living with MS than was previously thought.

Q: Where did the earlier MS prevalence number of 400,000 come from?
A: The previous figure of 400,000 was an estimate calculated from population growth since the national study of MS prevalence that was published in 1981.

Q. How did the prevalence number jump from 400,000 to 913,925?
A. As part of a Society-funded study, researchers developed a novel method for estimating the number of people who are living with MS using large medical claims datasets. This method has produced a higher, and likely more accurate, count.

Q: Why is this information important? And what does it mean for people affected by MS and the work of the National MS Society?
A: Having this scientifically sound prevalence estimate will facilitate a better understanding of the needs of people with MS and the economic burdens imposed by the disease on families and society. It will be a starting point for researchers to understand if MS is increasing, or if there are MS geographic clusters that hold clues to factors that trigger MS. These data will also help ensure that the National MS Society is able to connect to and support all people affected by MS.

Q: Does this mean more people are getting MS than before?
A. We don’t know. Since solid information on the number of people being diagnosed with MS has not been available, it has been difficult to tell whether more people are getting MS or if the total number is just a reflection of overall population growth, better diagnostic procedures, the availability of disease modifying drugs, or other changes in the MS landscape. Going forward, this should become easier. Outside of the U.S., some studies have reported increases in the incidence of MS. More work is needed to understand all the factors that led to this increase.

Q: What was the process to reach this new number and why has it taken so long to get an updated prevalence number of people living with MS in the U.S.?
A: After an examination of what it would take to identify a scientifically sound estimate, the Society funded the work and established a work group of experts across the fields of epidemiology, statistics and health care. This group labored for nearly four years to develop and implement a plan for estimating prevalence as rigorously as possible given the sources of information available. They obtained the proper mix of administrative datasets, developed and validated a formula to identify people with MS then applied it, and the findings were published in a peer-reviewed journal.

Q: Did this change the global number?
A: Yes, the global number is now 2.8 million (up from the previous estimate of 2.3 million). The global number is calculated through input from MS societies across the globe to the MS International Federation. Read more about the Atlas of MS.

Q: How confident are we in this number?
A: A team of experts led a thorough study based on a sound, scientific process and followed the peer-review process to affirm these results. We have trust and confidence in the approach and methodology that produced these results. In addition, the figures for the US are as high or higher than figures found in other countries using a variety of different methods to calculate the number.

Q: Will this new prevalence estimate help us get to a cure for MS faster?
A: Research breakthroughs related to what causes MS and how to cure it are happening at a faster pace than ever before. Having sound information on how many people are living with MS and who gets MS is an important pathway to a cure.

Q: When and how will the prevalence number be updated again?
A: The National Neurological Conditions Surveillance System, which was authorized in 2016 through the 21st Century Cures Act, has been funded and will be able to update prevalence estimates on a regular basis. This is a culmination of more than a decade of work by MS activists and others across the neurologic community. This system will provide important demographic data to help researchers move more quickly toward cures for the millions of people who live with diseases like MS and Parkinson’s.

Q: Why do we only have an estimate of the number of people with MS, versus knowing the exact figure?
A: Unlike for certain infectious disorders, there is no requirement for healthcare providers to report to health authorities when a person is diagnosed with MS. Although a nearly exact count could be made by contacting doctors, hospitals, and other health care facilities, such a study would be prohibitively expensive and almost impossible to implement.

Q: Will you be doing a study to help determine incidence of MS?
A: The National MS Society is not planning a study to determine the incidence of MS.

Q: When do we anticipate any results from the new CDC surveillance system?
A: We are not aware of a timeline at this point.

Q: What does this new number mean for the work of the National MS Society?
A: First and foremost, it means twice as many people need the Society to help them navigate the challenges of MS until we find a cure. This new number increases the urgency and importance of all areas of our work: we need to raise more money for research to find solutions, fund more programs and services to meet the needs of twice as many people, and fund advocacy to make sure our voices are twice as strong in legislative matters to represent all people living with MS; and we need to  make sure more people are connected to our MS Navigators so they can get the information and services they need.

Q: As a donor or fundraiser, how does this change the impact of my support?
A: Establishing an updated prevalence number will help us be more powerful in solving the challenges of MS and this breakthrough would not have been possible without your support—so we thank you! And now that we know that nearly 1 million people are living with MS in the U.S., it means your dollars need to work twice as hard and that we must find new ways to bring even more people into our movement.

Q: I live with MS or care about someone who does, what can I do to help the nearly 1 million people with this disease?
A: We are a movement by and for people affected by multiple sclerosis. We believe that we are stronger together, and we all have something to contribute—whether it’s time, money, connections or sheer passion. There is strength in numbers and we are calling on you to join us. Find your place in this movement. And when you meet someone with MS, make sure they’ve connected the National MS Society. Because we are here with the most comprehensive MS information in the world and are a supportive partner in addressing the challenges of this disease (call 800-344-4867 or visit


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