Since its clinical introduction in the early 1980s, MRI has transformed the practice of differential diagnosis and disease monitoring for disorders affecting the central nervous system, in particular multiple sclerosis and the allied inflammatory demyelinating diseases. Widespread and dynamic inflammatory processes of the white matter that were largely invisible by CT scanning now are rendered in exquisite detail by conventional MRI, and newer techniques are providing a wealth of information regarding axonal degeneration and functional adaptation. Overuse and over-reliance on MRI by clinicians sometimes can occur, and careful interpretation and clinical judgment remain essential in the care of multiple sclerosis.