The nature, prevalence, and course of cognitive and emotional disturbances in multiple sclerosis (MS) are described in this article. Mild to moderate cognitive impairment is common in MS and may be more incapacitating than physical symptoms for some patients. Although existing neurologic and neuroimaging procedures can detect some cognitively impaired patients, they lack sensitivity. Development of a brief neuropsychological screening battery, suitable for routine clinical use, is an important objective that may be achieved in the near future.