Forty-one patients with multiple sclerosis were studied with magnetic resonance imaging (MRI) and a battery of neuropsychological tests to determine the pattern of lobar distribution of lesions in the relapsing-progressive and relapsing-remitting forms of the disease. Correlation of lesions with the patient's cognitive and emotional dysfunction was also obtained. The results of this study indicate that patients with relapsing-progressive multiple sclerosis are characterized by the large or coalescent lesions located predominantly in the periventricular area. These lesions were more frequently found in the parietooccipital areas and were accompanied by significant cognitive dysfunction and severe personality changes. The patients with relapsing-remitting disease, however, were characterized by punctiform or small discrete lesions predominantly located in the intermediate and subcortical areas. These lesions were more frequently seen in the parietooccipital regions and the patients had significantly less severe cognitive and emotional involvement than did the patients with relapsing-progressive disease. Recognition of these patterns was easily accomplished by MRI. In this investigation MRI studies were utilized as an index of the pathological changes occurring at one point in time in the evaluation of the disease. Only repeated MRI studies and continuous clinical observation can establish the final diagnosis.