Modern neuroimaging, and in particular magnetic resonance imaging (MRI), has made a major contribution to the assessment of patients with multiple sclerosis. Brain MRI is the single most useful diagnostic investigation, and recent improvements in the quality of spinal cord imaging make MRI of this region a powerful tool in the evaluation of patients with undiagnosed myelopathies or with probable multiple sclerosis but equivocal findings on brain imaging. Putative MR markers of inflammation and axonal loss have, respectively, provided new insights into the mechanisms of relapse and remission on the one hand and persistent disability on the other. Monthly MRI is a powerful method for screening new therapies in relapsing-remitting and relapsing-progressive disease, but because of the uncertain relationship between short-term MRI activity and long-term disability, definitive trials should continue to have primary clinical endpoints.