What Is MS?

Find out how the immune system’s abnormal response damages the central nervous system, causing variable and unpredictable symptoms.

Learn how the immune system may interact with genetic, environmental and infectious factors to cause MS.

Nearly 1 million people are living with MS in the United States, according to a study funded by the National MS Society. This is more than twice the original estimate and means solutions for MS are now twice as important.

Learn the facts and figures — how many people have MS, and their location, age at diagnosis, gender, and ethnic background.

Get started with the basics with frequently asked questions about MS.

Explore the four disease courses to understand the similarities and differences between them.

Read about the other immune-mediated, demyelinating diseases of the central nervous system for which the Society offers information, resources and services.