The first class 1 treatment trial ever conducted in multiple sclerosis (MS) was a Veterans Administration Cooperative Study. This led us to explore MS in the military-veteran populations of the United States in three main series: Army men hospitalized with final diagnoses of MS in World War II, all veterans of World War II and the Korean Conflict, and veterans of later service up to 1994. In each series, all cases had been matched with pre-illness military peers. These series provide major information on its clinical features, course and prognosis, including survival, by sex and race (white men and women; black men), as well as risk factors for occurrence, course, and survival. They comprise the only available nationwide morbidity distributions of MS in the United States. Veterans who are service-connected for MS by the Department of Veterans Affairs and matched with their military peers remain a unique and currently available resource for further clinical and epidemiological study of this disease.