We identified 5345 cases of multiple sclerosis (MS) among US veterans who first entered military service between 1960 and 1994, and who were "service-connected" for MS by the Department of Veterans Affairs (VA). Two controls per case were matched on age, date of service entry, and branch of service. Available for service and VA files were demographic and military data for 4951 cases and 9378 controls. Versus white men, relative risk of MS was significantly higher for all women, at 2.99 for whites, 2.86 for blacks, and 3.51 for those of other races. This was a significant increase from our prior series of veterans of World War II and the Korean Conflict, where white women had a relative risk of 1.79. Risk for black men was higher now (0.67 vs 0.44), while other men remained low (0.30 vs 0.22). Residence at service entry in the northern tier of states had a relative risk of 2.02 versus the southern tier, which was significantly less than the 2.64 for the earlier series. Residence by individual state at birth and service entry for white men further supported this decreasing geographic differential. Such marked changes in geography, sex, and race in such a short interval strongly imply a primary environmental factor in the cause or precipitation of this disease.