Because multiple sclerosis has always been considered a disorder of the central nervous system white matter, sparing the gray matter, cognitive dysfunction was believed to be rare in multiple sclerosis. However, the data do not support this. Over 40% of the patients with multiple sclerosis have cognitive impairment. The cognitive symptoms are not the classical symptoms of dementia but are primarily manifested in decreases in attention, speed of information processing, memory, and executive functions. Although there is often a decrement in IQ, it relates more to the performance portion of the WAIS and often improves with remission of the multiple sclerosis. Dr. Feinstein notes, quite justifiably, that the commonly used Mini-Mental State is very poor in picking up the cognitive impairments manifested by multiple sclerosis patients. He goes on to discuss the utility of other neuropsychological tests. There is also a very useful review of other conditions where subcortical dementia has been observed, such as Huntington’s disease, HIV infection, and Binswanger’s disease. Comparing the findings in these conditions with those in multiple sclerosis, Dr. Feinstein he builds a good case for the concept of subcortical dementia.