In multiple sclerosis, behavioral changes, including alterations in cognitive functions and psychiatric abnormalities, have been recognized with increasing frequency in recent years. Multiple sclerosis formerly was thought to be primarily a disorder of the brain stem and spinal cord; however, functional changes that can be attributed, at least in part, to cerebral dysfunction are being recognized. Certain cognitive functions such as memory and conceptual processes seem to be preferentially impaired. The degrees of impairment of other functions such as attention and visuospatial skills are now being evaluated. Psychiatrically, affective disorders seem to be the most common diagnoses, and debate exists about whether these abnormalities are a function of the demyelinating process itself or are a reaction to the disability produced by the disorder.