This study compared the intellectual deficits of patients who had the earliest stages of Huntington's disease (HD) with those of mildly or moderately affected patients suffering from multiple sclerosis; both groups were matched for age, education, and ability to function. Twenty-one HD patients, 30 multiple sclerosis subjects, and 15 matched controls were evaluated neuropsychologically; all were free of psychoactive medications. The two patient groups showed similar overall patterns of impairment, though the HD group had greater verbal and nonverbal memory deficits. The HD patients also demonstrated significant dyscalculia and showed indications of developing problems in language usage and copying. These results are discussed in light of each disorder's neuropathologic substrate.