Multiple sclerosis (MS) is a common cause of disability in young adults. Establishing a definitive diagnosis of the disease is often difficult, and there is much uncertainty concerning prognosis once the diagnosis is made. Magnetic resonance imaging (MRI) studies have proved to be a useful diagnostic test in the initial evaluation and monitoring of patients with MS. They also provide a means for quantitative assessment of disease activity and progression during clinical trials of MS therapies. Improvements in MRI technology show promise in providing more accurate measurements of disease extent. The new technique of magnetic resonance spectroscopy can be used to monitor the specific pathophysiology of evolving MS plaques in vivo and may provide insights that lead to a better understanding of the pathogenesis of MS.