The performance of 38 patients with chronic progressive multiple sclerosis was compared with that of 26 age- and education-matched controls on a battery of tests of information-processing speed, verbal fluency, naming, egocentric perception, and anterograde and remote memory. Although there were marked differences in the extent and severity of cognitive disturbance among individual patients, as a group they were impaired compared with controls on all measures. Deficits were most striking on the Symbol-Digit Modalities Test and the verbal fluency measures, tests that require rapid information processing. More than 75% of the patients scored below the tenth percentile for controls on the Symbol-Digit Modalities Test, while 61% scored below the tenth percentile on verbal fluency. Memory disturbances were also common. More than 45% of the patients scored below the tenth percentile. The proportion of impaired patients was quite similar for anterograde and remote memory tests and for recall and recognition procedures. The pattern of memory disturbance and slowed information processing resembled deficits generally observed in subcortical dementias, such as Huntington's disease, but in addition, the patients with multiple sclerosis showed naming difficulties that are usually associated with cortical dementias, such as Alzheimer's disease.