RELATIVELY few, and no continuous, electroencephalographic studies appear to have been made of patients with multiple sclerosis. The object of the present work is to investigate and discuss to what extent the electroencephalogram reflects the activity, duration, localization, and gravity of the disease. MATERIAL AND METHOD The material comprises 74 inpatients and outpatients and is probably fairly representative of the disease. Forty-four patients were females and 30 were males. Eleven, or 15%, were less than 30 yr. of age, 2 being under 20 yr.; 37, or 50%, were 31 to 40 yr. of age, and 26, or 35%, were more than 40. Fourteen, or 19%, had been ill less than two years; 17, or 23%, from two to five years; 20, or 27%, from five to 10 yr., and 23, or 31%, more than 10 yr. The general gravity of the symptoms, expressed roughly in terms of occupational capacity, (corrected