Multiple sclerosis (MS) is the most common cause of neurological disability in young European and North American adults. It is defined as dysfunction in different parts of the central nervous system at different points in time. The etiology is likely autoimmune, resulting from environmental and genetic factors. This article summarizes the symptoms, progression, diagnosis, and treatment of MS. MRI and CSF studies have been extremely helpful in identifying individual cases, but the diagnosis remains a clinical diagnosis, and one of exclusion. Methylprednisolone remains the preferred treatment for acute relapses, although plasma exchange has been shown to be helpful in cases when methylprednisolone has failed. Preventive immunomodulatory treatments are the focus of many current research efforts. Although these treatments have been shown to reduce the frequency of MS attacks, the reduction is modest, at 30%. The data that these drugs alter the progression of disability is less compelling.