Neuropsychological and neuroradiologic evidence of cerebral lesions is described for 12 patients with multiple sclerosis in whom cognitive disability was far greater than any other neurologic disability. Cognitive dysfunction resulted in significant functional impairment at work or home in three fourths (9 of 12) of the patients described here, despite mild physical disability (mean Kurtzke Expanded Disability Status Scale score, 3.2). A unique feature of the neurologic examination in these patients was the presence of prominent frontal release signs (gait apraxia and placing response) in the lower extremities. Two new scales, a Cognitive Function Scale and a Frontal Release Scale, were adapted for the investigation of these patients. The extensive literature relating to cognitive dysfunction in multiple sclerosis is reviewed and discussed with regard to its clinical relevance.