Studies performed under 89-N-0045 are designed to examine the natural history of multiple sclerosis (MS) using MRI and immunological measures. In addition to studying the natural history of untreated patients, the natural history of patients receiving approved disease-modifying therapies of MS will be examined. In both cohorts of patients levels of disease activity on MRI will be compared with immunological characteristics in order to help identify disease mechanism. Patients with either definite MS (based either on clinical or combined clinical and MRI criteria) or with an initial presentation of neurological dysfunction consistent with MS will be studied longitudinally by MRI. Disease activity on MRI will be assessed using several MRI measures of disease activity including the number of contrast enhancing lesions, the overall burden of disease, brain atrophy and measures to assess axonal damage. Patients will be assessed clinically and correlations between immunological and genetic factors and disease activity as seen clinically or by MRI will be studied.