Creutzfeldt-Jakob disease (CJD) has been transmitted in the laboratory and also by iatrogenic accident. However, research has failed to find evidence that its most common form (sporadic CJD) is a natural infection and, in particular, that there is a causal link with scrapie. Bovine spongiform encephalopathy (BSE) probably resulted from scrapie infection in cattle food. In the wake of the BSE epidemic, a novel clinico-pathological form of CJD has been recognized: new variant CJD (nvCJD). This paper reviews the relationship between nvCJD and BSE and presents the accumulated evidence supporting the view that nvCJD resulted from BSE contamination of human food.