About 10 years after bovine spongiform encephalopathy (BSE) appeared in British cattle, a new variant of Creutzfeldt-Jakob disease (nv-CJD) was described in the United Kingdom. This new disease is distinguishable from classical CJD in its aetiology, epidemiology, clinical profile, and neuropathology. The emergence of nv-CJD raised fears of a causal relationship between BSE and nv-CJD and of a human epidemic of indeterminate size. This paper reviews our knowledge of this group of diseases, and examines recent scientific evidence, which indicates that BSE is indeed the source of nv-CJD, and discusses the public health implications.