Though the global course of the disease is well known when considering large cohorts of patients, it is rather difficult to make a prognosis for a given patient. It is essential however to predict the course of the disease as early as possible in order to be able to give the patient the right treatment at the right time. Age at disease onset is one of the most important clinical predictive factors, as this has been proved by various analyses. The earlier the disease onset, the better the prognosis. The inaugural symptom of optic neuritis, the long interval between the first two relapses, a remitting form at onset are predictive factors of a good evolution. A normal brain magnetic resonance imaging performed on the occasion of a first isolated sign of the central nervous system is the marker of a good prognosis. Conversely, the presence of oligoclonal bands in the cerebrospinal fluid and the increase of IgG index increase the risk of occurrence of a second relapse. The new techniques of magnetic resonance imaging and the exhaustive initial clinical examination using several classifications of disability will allow a better prognosis for a given patient.