The diagnosis and management of patients with Multiple Sclerosis (MS) requires magnetic resonance imaging (MRI), that should be acquired according to a standardized and reproducible protocol, consistent with international guidelines. Hyperintensities on T2 or FLAIR sequences are a very sensitive finding in patients with MS but is not specific of the underlying pathology. Cerebral atrophy occurs very early in the course of the disease. Among patients with clinically isolated syndromes, the presence of spatially disseminated lesions on the initial MRI is highly predictive of the conversion to clinically definite MS. The correlations between clinical findings and radiological abnormalities identified on MRI conventional sequences remain poor, as conventional MRI doesn't accurately quantify the microscopic damage in normal appearing brain tissue. New sequences such as MR spectroscopy, diffusion tensor imaging, magnetization transfer imaging allow more sensitive quantification of such alterations. Molecular imaging by Positrons Emission Tomography is a very promising technique with high tissue specificity. It should improve our understanding of the pathophysiologic mechanisms involved in MS.