Multiple sclerosis (MS) affects different people in different ways. For people who have only mild symptoms from time to time, the disease may not have much impact on their everyday lives. People with more severe MS have frequently recurring or ongoing symptoms and may become disabled within a few years.

Most people with MS are between these extremes. For them, MS involves a series of attacks that cause symptoms. These attacks are called relapses, flares, or exacerbations. They may last for days or weeks and then partially or completely go away. Relapses may be mild or severe and tend to recur over a period of years. They may become worse and more frequent over time, with symptoms becoming more severe and disabling. For most people with MS, the disease follows a relapsing-remitting course, at least at first. Up to half of people with relapsing-remitting MS may develop secondary progressive MS within 10 years.

A diagnosis of MS can be difficult to accept for the thousands of healthy, active people whom the disease strikes without warning. Though rarely life-threatening, MS has no cure. Most people live with the disease for decades. However, many face increasing disability as they get older.