Between 1949 and 1984, 150 multiple sclerosis patients consumed low-fat diets. Fats, oils, and protein intakes; disability; and deaths were determined. On daily fat consumption of less than 20.1 g (average 17 g), 31% died and deterioration was slight. Daily intakes of greater than 20 g (average of either 25 or 41 g) were attended by serious disability and deaths of 79% and 81%, respectively. Oil intakes bore an indirect relationship to fat consumption. Treatment early and before severe disability developed improved prognosis, and females tended to do better than males.