Strong epidemiologic and laboratory evidence indicate that a novel, variant form of Creutzfeldt-Jakob disease (vCJD) first reported in the United Kingdom in 1996 is causally linked with bovine spongiform encephalopathy (BSE). BSE was first identified in the early 1980s in the United Kingdom, and has since spread to other European countries and recently to Japan and Israel. Although the United Kingdom BSE epizootic is on the decline, widespread exposure of humans to infected cattle products may have already occurred, raising concerns about the ultimate magnitude of the vCJD outbreak which, as of October 2002, has already affected 138 patients worldwide, including 128 patients in the United Kingdom.